Python cheat sheet

python_cheat_sheet.txt

#PyPI
Is the module repository in Python (the equivalent to CPAN in Perl)

//
*Initializing 2 variables at the same time:
a=b=0

or

a=b=0.0
//
#Python shebang:
#!/usr/bin/env python (for python 2.7 latest)
#!/usr/bin/env python3 (for python 3.latest)

# Python style guide:
https://www.python.org/dev/peps/pep-0008/

*Class Names:
Class names should normally use the CapWords convention

*Funcƒtion Names;
Function names should be lowercase, with words separated by
underscores as necessary to improve readability.

*Function params:
The most followed convention is the one used in NumPy (described at
https://github.com/numpy/numpy/blob/master/doc/HOWTO_DOCUMENT.rst.txt)

Parameters
----------
x : type
    Description of parameter `x`.
y
    Description of parameter `y` (with type not specified)

#to print
print "hello";
/
#python naming conventions
-Class names start with an uppercase letter. All other identifiers start with a lowercase letter.
-Starting an identifier with a single leading underscore indicates that the identifier is private.
- Starting an identifier with two leading underscores indicates a strongly private identifier.
- If the identifier also ends with two trailing underscores, the identifier is a language-defined special name.
#assign values to variableswh
counter = 100          # An integer assignment
miles   = 1000.0       # A floating point
name    = "John"       # A string
//
#Object introspection:

my_list = [1, 2, 3]
dir(my_list)
#gave us the names of all the methods of a list. This can be handy when you are not able to recall a method name.
/
#using type:
print(type(''))
# Output: <type 'str'>
/
#Using Inspect:
import inspect
print(inspect.getmembers(str))


#multiple assignment
a = b = c = 1

a, b, c = 1, 2, "john"

#increment operator
a+=2

#print variables
print counter
print miles
print name

#Standard Data Types
Numbers
String
List
Tuple
Dictionary
/
#knowing the data type of some object:
type(whatever)

#Python strings:
str = 'Hello World!'

print str[0]; #print H
print str[1:3]; #print el
print str[2:]; #print llo (everything from the 2nd character)
print str*2; #prints hellohello
print str1+str2 #concatenating 2 strings

#concatenating a string and a number, where b is the number:
str=a+str(b)

#python lists:
list = [ 'abcd', 786 , 2.23, 'john', 70.2 ]

print list          # Prints complete list
print len(list) #print length of list
print list[0]       # Prints first element of the list
print list[1:3]     # Prints elements starting from 2nd to 4th
print list[2:]      # Prints elements starting from 3rd element
print tinylist * 2  # Prints list two times
print list + tinylist # Prints concatenated lists      

#adding a prefix to each element on a list:
alist = ['foo','spam', 'bar']
prefix='pref'

newlist=[prefix+elt for elt in alist]

#print join a list
mylist = ['spam', 'ham', 'eggs']
print ','.join(mylist)

*Remove an element's first occurrence  in a list
>>> a = ['a', 'b', 'c', 'd']
>>> a.remove('b')
>>> print a
['a', 'c', 'd']

#remove duplicated elements from list
mylist = ['spam', 'ham', 'eggs']
set(mylist)
//
#sets in python.
#read list of words in a file into a set:
my_set = set(open('all_runs.ega.txt'))
/
#this will contain a trailing \n, so we need to do the following:
set(line.strip() for line in open('filename.txt'))
//
#A good way of checking what elements there is in one list and not the
other and vice versa:
To find the intersection (items that are in both sets):

>>> a = set([1, 2, 3, 4, 5, 6])
>>> b = set([4, 5, 6, 7, 8, 9])
>>> a & b
set([4, 5, 6])
To find the difference (items that only in one set):

>>> a = set([1, 2, 3, 4, 5, 6])
>>> b = set([4, 5, 6, 7, 8, 9])
>>> a - b
set([1, 2, 3])
>>> b - a
set([7, 8, 9])
To find the symmetric difference (items that are in one or the other, but not both):

>>> a = set([1, 2, 3, 4, 5, 6])
>>> b = set([4, 5, 6, 7, 8, 9])
>>> a ^ b
set([1, 2, 3, 7, 8, 9])
/
*Adding elements to a set
>>> a.add(7)
//
#python tuples:
A tuple is another sequence data type that is similar to the list. A tuple consists of a number of values separated by commas. Unlike lists, however, tuples are enclosed within parentheses.
Tuples can be thought of as read-only lists.
tuple = ( 'abcd', 786 , 2.23, 'john', 70.2  )
tinytuple = (123, 'john')

print tuple           # Prints complete list
print tuple[0]        # Prints first element of the list
print tuple[1:3]      # Prints elements starting from 2nd to 4th
print tuple[2:]       # Prints elements starting from 3rd element
print tinytuple * 2   # Prints list two times
print tuple + tinytuple # Prints concatenated lists
//
#list of tuples
my_list = [ ('a', 1), ('b', 2), ('c', 3), ('d', 4)]
//
#iterating over list of tuples:
for j,k in my_list:
...     print j
...     print k
/
*named tuples:
from collections import namedtuple
Point = namedtuple('Point', 'x y')
pt1 = Point(1.0, 5.0)
pt2 = Point(2.5, 1.5)

from math import sqrt
line_length = sqrt((pt1.x-pt2.x)**2 + (pt1.y-pt2.y)**2)
//
#Python Dictionary:
Python 's dictionaries are hash table type. They work like associative arrays or hashes found in Perl and consist of key-value pairs.

tinydict = {'name': 'john','code':6734, 'dept': 'sales'}
print dict['one']       # Prints value for 'one' key
print dict[2]           # Prints value for 2 key
print tinydict          # Prints complete dictionary
print tinydict.keys()   # Prints all the keys
print tinydict.values() # Prints all the values

//
#compare 2 dictionaries

Make Two Dictionaries
importers = {'El Salvador' : 1234,
             'Nicaragua' : 152,
             'Spain' : 252
            }

exporters = {'Spain' : 252,
             'Germany' : 251,
             'Italy' : 1563
             }
Find Duplicate Keys
# Find the intersection of importers and exporters
importers.keys() & exporters.keys()
{'Spain'}
Find Difference In Keys
# Find the difference between importers and exporters
importers.keys() - exporters.keys()
{'El Salvador', 'Nicaragua'}
Find Key, Values Pairs In Common
# Find countries where the amount of exports matches the amount of imports
importers.items() & exporters.items()
{('Spain', 252)}
//
# Merge 2 dictionaries (dicts)
>>> x = {'a': 1, 'b': 2}
>>> y = {'b': 3, 'c': 4}

>>> z = {**x, **y}

>>> z
{'c': 4, 'a': 1, 'b': 3}

#When there are 2 overlapping keys then the right-hand key has precedence
//
#if
if expression:
   statement(s)

#else
if expression:
   statement(s)
else:
   statement(s)	

#elif
if expression1:
   statement(s)
elif expression2:
   statement(s)
elif expression3:
   statement(s)
else:
   statement(s)

#and operator
if (expression1 and expression2):
   statement(s)

#while loop
while expression:
   statement(s)

#for statement
for iterating_var in sequence:
   statements(s)
ex:
l=[1,2,3,4,5,6]
for i in l:
    print i
ex:
for i in 'caca':
    print i

#break statement
for letter in 'Python':     # First Example
   if letter == 'h':
      break
   print 'Current Letter :', letter
  
var = 10                           # Second Example
while var > 0:              
   print 'Current variable value :', var
   var = var -1
   if var == 5:
      break

print "Good bye!"

#continue statement
for letter in 'Python':     # First Example
   if letter == 'h':
      continue
   print 'Current Letter :', letter

var = 10                    # Second Example
while var > 0:              
   print 'Current variable value :', var
   var = var -1
   if var == 5:
      continue

print "Good bye!"
//
'''
 Iterate over the list using while loop
'''
i = 0
sizeofList = len(wordList) 
while i < sizeofList :
    print(wordList[i]) 
    i += 1
//
#defining a function and calling function
#!/usr/bin/python

# Function definition is here
def printme( str ):
   "This prints a passed string into this function"
   print str;
   return;

# Now you can call printme function
printme("I'm first call to user defined function!");
printme("Again second call to the same function");

#opening a file for writing
>>>f = open('workfile', 'w')
>>>print f
<open file 'workfile', mode 'w' at 80a0960>

#opening a file for reading and printing lines
f=open('/Users/ernesto/supercont1.1v4.gff','r');
for line in f:
        print line,
//
# open a file if provided, if not then write to STDOUT
import sys
import contextlib

@contextlib.contextmanager
def smart_open(filename=None):
    if filename and filename != '-':
        fh = open(filename, 'w')
    else:
        fh = sys.stdout

    try:
        yield fh
    finally:
        if fh is not sys.stdout:
            fh.close()

Use it like this:
# writes to some_file
with smart_open('some_file') as fh:
    print >>fh, 'some output'

# writes to stdout
with smart_open() as fh:
    print >>fh, 'some output'

# writes to stdout
with smart_open('-') as fh:
    print >>fh, 'some output'


//
#opening a file and write something
f=open('text.txt','w');
f.write("hello");
f.close;
/
#adding a newline:
f.write(your_string+"\n");
/
#append a text
f=open('text.txt','a');
f.write("hello");
f.close;

#create a dir
import os;
os.mkdir("newdir");

#change into a dir
os.chdir("newdir");

#split a string
>>> str="hello,bye"
>>> str.split(',')
>>> str
['hello', 'bye']

#split string into elms using tab separators
elms=line.split("\t")	

#replace text in a string
>>> s = '100 NORTH MAIN ROAD'
>>> s.replace('O','U')
'100 NURTH MAIN RUAD'

#regex

#1st ex:import re;

m = re.search("(\d+)","hello 12 bye caca")

if m:
    print m.groups()[0]
>>>12

#combining a patther and a variable
m1=re.search(r'>+%s' %variablename,line)

#finding all occurences of a pattern
>>> import re;
>>> p = re.compile('\d+');
>>> p.findall('12 drummers drumming, 11 pipers piping, 10 lords a-leaping')
['12', '11', '10']

#finding all declaring the pattern in the same line
>>> import re;
>>> re.findall('\d+','12 drummers drumming, 11 pipers piping, 10 lords a-leaping')

#checking if a string is empty
if not myString:
   do something....

#checking if a string starts with '>'
import re;

p = re.compile( '^>' )
m = p.match( '>hello' )
if m:
    print 'Match found: ', m.group()
else:
    print 'No match'

>>>Match found:  >

Another simpler way:

m=re.search("^>",line)
if m:
    print 'Match found: ', m.group()

#matchin more than one pattern on the same string
m=re.search("^>|^#",line)
if m:
    print 'Match found: ', m.group()

#matching all non ACGT bases in a DNA sequence:
import re


dna = "ATCGCGAZZZTTCAA"
if re.search(r"[^ATGC]", dna):
    print("restriction site found!")
//
#Counting longest occurrence of repeated sequence in Python

import re
my_str = "abcdefgfaabbbffbbbbbbfgbb"
length=len(max(re.compile("(b+b)*").findall(my_str)))
print(length)

/
#negating a specific pattern
patt = re.compile('(?!_NON_REF)_GENOTYPE_CONCORDANCE' )

//
#exit from a program
sys.exit(0)

#accessing the command line args
import sys

print 'Number of arguments:', len(sys.argv), 'arguments.'
print sys.argv[0] #print script name
print sys.argv[1] #printing first arg

#exiting if number of args is incorrect
if (len(sys.argv)<3):
    sys.exit("[USAGE] python test_1.py <gff> <gene_id>") 
//
#most efficient way of parsing command line args:
Good tutorial at:
https://mkaz.tech/python-argparse-cookbook.html
/
#First example using a single verbose 
import sys
import argparse

parser = argparse.ArgumentParser(description='Demo')
parser.add_argument('--verbose',
    action='store_true',
    help='verbose flag' )

args = parser.parse_args()

if args.verbose:
    print("~ Verbose!")
else:
    print("~ Not so verbose")
#This is run by:
$ python test.py
~ Not so verbose

$ python test.py --verbose
~ Verbose!
#if you run it with 
 python test.py --help 
#you will get:
usage: generate_expPer_donor.py [-h] [--verbose]

Demo

optional arguments:
  -h, --help  show this help message and exit
  --verbose   verbose flag
/
#required arg:
parser = argparse.ArgumentParser()
parser.add_argument('--limit', required=True, type=int)
args = parser.parse_args()

/
#Parsing a file argument:
parser = argparse.ArgumentParser()
parser.add_argument('f', type=argparse.FileType('r'))
args = parser.parse_args()

for line in args.f:
    print( line.strip() )
//
#validating arguments
def check_positive(value):
    ivalue = int(value)
    if ivalue <= 0:
        raise argparse.ArgumentTypeError("%s is an invalid positive int value" % value)
    return ivalue

parser = argparse.ArgumentParser(...)
parser.add_argument('foo', type=check_positive)
//
#adding a default value for an option:
parser.add_argument('--limit', default=5, type=int)
//
#removing \n in python:
'test string \n'.rstrip('\n')
or
line=line.rstrip('\n')
//
#using a list as an option for argparse:
parser.add_argument('-l','--list', nargs='+', help='<Required> Set flag', required=True)
# Use like:
# python arg.py -l 1234 2345 3456 4567
# 	 
TL;DR

Use the nargs option or the 'append' setting of the action option (depending on how you want the user interface to behave).

nargs

parser.add_argument('-l','--list', nargs='+', help='<Required> Set flag', required=True)
# Use like:
# python arg.py -l 1234 2345 3456 4567
nargs='+' takes 1 or more arguments, nargs='*' takes zero or more.
//
#OOP in Python
//
A Python file is called a "module" and it's one way to organize your software so that it makes "sense". Another is a directory, called a "package".

A module is a distinct thing that may have one or two dozen closely-related classes. The trick is that a module is something you'll import, and you need that import to be perfectly sensible to people who will read, maintain and extend your software.

The rule is this: a module is the unit of reuse.

//
#!/usr/bin/python

class Employee:
   'Common base class for all employees'
   empCount = 0

   def __init__(self, name, salary):
      self.name = name
      self.salary = salary
      Employee.empCount += 1
   
   def displayCount(self):
     print "Total Employee %d" % Employee.empCount

   def displayEmployee(self):
      print "Name : ", self.name,  ", Salary: ", self.salary

"This would create first object of Employee class"
emp1 = Employee("Zara", 2000)
"This would create second object of Employee class"
emp2 = Employee("Manni", 5000)
emp1.displayEmployee()
emp2.displayEmployee()
print "Total Employee %d" % Employee.empCount
/
#Inheritance:
class MinimumBalanceAccount(BankAccount):
    def __init__(self, minimum_balance):
        BankAccount.__init__(self)
        self.minimum_balance = minimum_balance

    def withdraw(self, amount):
        if self.balance - amount < self.minimum_balance:
            print 'Sorry, minimum balance must be maintained.'
        else:
            BankAccount.withdraw(self, amount)
#Where BankAccount is the parent class and withdraw overrides the
        withdraw method in the parent class
/
*Another example of inheritance:
class Person:

    def __init__(self, first, last):
        self.firstname = first
        self.lastname = last

    def __str__(self):
        return self.firstname + " " + self.lastname

class Employee(Person):

    def __init__(self, first, last, staffnum):
        super().__init__(first, last)
        self.staffnumber = staffnum


x = Person("Marge", "Simpson")
y = Employee("Homer", "Simpson", "1007")

print(x)
print(y)

/
#class built-in methods
__doc__ #class documentation, for examples;
print Employee.__doc__
/
#inheritance
#!/usr/bin/python

class Parent:        # define parent class
   parentAttr = 100
   def __init__(self):
      print "Calling parent constructor"

   def parentMethod(self):
      print 'Calling parent method'

   def setAttr(self, attr):
      Parent.parentAttr = attr

   def getAttr(self):
      print "Parent attribute :", Parent.parentAttr

class Child(Parent): # define child class
   def __init__(self):
      print "Calling child constructor"

   def childMethod(self):
      print 'Calling child method'
/
*Set attribute:
setattr(x, attr, 'magic')
/
*Initializing an object from a dict:
for k,v in c.items():
    setattr(self,k,v)
    print "h"
/
# Private methods and attributes in Python:
# The information below is extracted from https://www.bogotobogo.com/python/python_private_attributes_methods.php
#
# Example of a class:
# p.py
class P:
   def __init__(self, name, alias):
      self.name = name       # public
      self.__alias = alias   # private

   def who(self):
      print('name  : ', self.name)
      print('alias : ', self.__alias)

# When we create an instance of P and we try to access its attributes:
>>> from p import P
>>> x = P(name='Alex', alias='amen')
>>> x.name
'Alex'
>>> x.alias
Traceback (most recent call last):
  File "", line 1, in 
AttributeError: P instance has no attribute 'alias'
# We can't access alias using double underscore:
>>> x.__alias
Traceback (most recent call last):
  File "", line 1, in 
AttributeError: P instance has no attribute '__alias'
# But we can access by using a single underscore:
>>> x._P__alias
'amen'
# We can also have Private functions. An example of a class:
# p2.py
class P:
   def __init__(self, name, alias):
      self.name = name       # public
      self.__alias = alias   # private

   def who(self):
      print('name  : ', self.name)
      print('alias : ', self.__alias)

   def __foo(self):          # private method
      print('This is private method')

   def foo(self):            # public method
      print('This is public method')
      self.__foo()
 # We can instantiate the class, but when we try to access the
 # private function:
 >>> from p2 import P
>>> x = P('Alex', 'amem')
>>> x.__foo()
Traceback (most recent call last):
  File "", line 1, in 
AttributeError: P instance has no attribute '__foo'
# But we can access this function by doing:
>>> x._P__foo()
This is private method
/
#debugging in python
# epdb1.py -- experiment with the Python debugger, pdb
import pdb
a = "aaa"
pdb.set_trace()
b = "bbb"
c = "ccc"
final = a + b + c
print final

Then, run the script and it will stop when it reaches the
pdb.set_trace() line.

After that press 'n+enter' to advance,
Also use 'p variable' to print the variable
Use 'l' to list where you are
Use b 48 (to set a breakpoint at  line 48)
Use c (go to the next breakpoint)
cl or clear #to clear all breakpoints
//
pretty printing a data structure in python (similar to Data::Dumper)
>>> import pprint
>>> stuff = ['spam', 'eggs', 'lumberjack', 'knights', 'ni']
>>> stuff.insert(0, stuff[:])
>>> pp = pprint.PrettyPrinter(indent=4)
>>> pp.pprint(stuff)
[   ['spam', 'eggs', 'lumberjack', 'knights', 'ni'],
    'spam',
    'eggs',
    'lumberjack',
    'knights',
    'ni']
//
#Object instrospection, using a customized way of printing the object:
>>> class Test:
...     def __repr__(self):
...         return "Test()"
...     def __str__(self):
...         return "member of Test"
... 
>>> t = Test()
>>> t
Test()
>>> print t
member of Test
/ One example of its real use:
class Test:
    def __init__(self, a, b):
        self.a = a
        self.b = b

    def __repr__(self):
        return "<Test a:%s b:%s>" % (self.a, self.b)

    def __str__(self):
        return "From str method of Test: a is %s, b is %s" % (self.a, self.b)
//
*print all the attributes of an object
def __str__(self):
    sb = []
    for key in self.__dict__:
        sb.append("{key}='{value}'".format(key=key, value=self.__dict__[key]))
 
    return ', '.join(sb)
 
def __repr__(self):
    return self.__str__() 

//
#printing contents of a Python dict within a debugger:
from pprint import pprint
pprint (vars(your_object))
//
#escaping in python:
print(r"\t\n")
#r stands for raw, this statement would literally print:
\t\n

#count characters within a string
dna="AAAAGGGGG"
dna.count("A")
dna.count("G")

#representation of an object
repr(objectname)
//

Initializing 2 variables at the same time
v1,v2=1,2
//
#        #
#debugger#
#        #
python -m pdb script.py #run python debugger
p variable #print variable contents
n #next statement
b 2 #create a breakpoint at line 2
/
if after entering a command we press enter, we repeat this last command
/
l #lists the area of my program that is currently being executed
/
s #step into a subroutine
/
q #exit from the debugger
/
c #continue until the next breakpoint is hitted
//
print 'hello'
//
>>>print 1,2 #print adding a space between
1 2
//
print 1,2, #print without newline at end of text
//
>>>a="ccc"
>>>print a.upper()
CCC
//
L1=[2,3,4] #create list (array)
print L1[0] #printing element at index=0
//
L1[-2] #accessing element but counting from the right
//
L1[2:] #slicing a list (from index at 2 until the last index)
//
values = [100, 200, 300, 400, 500]
# Slice from third index to index one from last.
slice = values[2:-1]
print(slice)

Output

[300, 400]
//
# different examples of slicing:
# Let us first create a list to demonstrate slicing 
# lst contains all number from 1 to 10 
lst = range(1, 11) 
print lst 
# we get:
range(1, 11)
That can be unpacked to:
lst = [*range(1, 11)] 

  
#  below list has numbers from 2 to 5 
lst1_5 = lst[1 : 5] 
print lst1_5 
  
#  below list has numbers from 6 to 8 
lst5_8 = lst[5 : 8] 
print lst5_8 
  
#  below list has numbers from 2 to 10 
lst1_ = lst[1 : ] 
print lst1_ 
  
#  below list has numbers from 1 to 5 
lst_5 = lst[: 5] 
print lst_5 
  
#  below list has numbers from 2 to 8 in step 2 
lst1_8_2 = lst[1 : 8 : 2] 
print lst1_8_2 
  
#  below list has numbers from 10 to 1 
lst_rev = lst[ : : -1] 
print lst_rev 
  
#  below list has numbers from 10 to 6 in step 2 
lst_rev_9_5_2 = lst[9 : 4 : -2] 
print lst_rev_9_5_2
//
# get the last elements of a list in python
>>> a = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]
>>> a
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]
>>> a[-9:]
[4, 5, 6, 7, 8, 9, 10, 11, 12]
//
L1=["c","a","c","a"] #create list with strings
//
enumerate function, how it works:
seasons = ['Spring', 'Summer', 'Fall', 'Winter']
 for i, item in enumerate(L):
...     print i
...     print item
0
Spring
1
Summer
2
Fall
3
Winter

//
#split a string into characters
>>>print list("hello")
['h', 'e', 'l', 'l', 'o']
//
#indexing strings
>>>h="hola"
>>>print h[0]
h
or
>>>print h[0:2]
ho
//
a="hola"
print len(a) #print out length of a
//
#concatenate
a="cac"
b="otas"
print a+b
//
>>>a="1"
>>>print a.isdigit()
True
\
>>> b="ahola"
>>> print b.isdigit()
False
isdigit() returns True if all characters in a string are digits
//
#print a list as a string
>>>L1=["c","a","c","a"]
>>>print','.join(L1)
c,a,c,a
//
#join in python 3
>>> ".".join(("a","b","c"))
'a.b.c'
//
#join in for loop:
url = 'http://ergast.com/api/f1/{0}/qualifying?limit=10000'

print('\n'.join(url.format(year) for year in range(2000, 2016)))

# http://ergast.com/api/f1/2000/qualifying?limit=10000
# http://ergast.com/api/f1/2001/qualifying?limit=10000
# ...
# http://ergast.com/api/f1/2015/qualifying?limit=10000
//
#print argv passed to the script (sys.argv is a list)
import sys
print sys.argv
print len(sys.argv) #length of the list
passedFile=sys.argv[1]
//
print 3 in [1,2,3] #check membership
'TRUE'
//
for x in [1,2,3]: print x #iterate list
//
#to iterate over a certain range(from,to,interval)
>>>for i in range(0,3,1):
>>>    print i
//
Generate list of range tuples with given boundaries in python

ranges = [(n, min(n+step, stop)) for n in xrange(start, stop, step)]

Will produce something like:
[(100, 110), (110, 120), (120, 130), (130, 140)]
//
#iterave over a list
>>>list=[1,2,3,4,5]
>>>for i in range(len(list)):
...     print list[i]
1 2 3 4 5

//
#append an elements into a list
list=[1,2,3]
list.append(4)
//
#append several elements onto list
list=[1,2,3]
list.extend([4,5,6])
//
#delete and print last element(item)
list=[1,2,3]
print list.pop()
//
#getting the last element of a list:
some_list[-1]
//
#reverse a list
# See methods at https://www.geeksforgeeks.org/python-reversing-list/
list.reverse()
//
#initializing an empty dict
newdict=dict()
//
#create dictionary (hash)
d1={'spam':2,'ham':1,'eggs':3}
//
#create dict from 2 lists:
keys = ['a','b','c','d'] 
values = [1,2,3,4]

d = dict(zip(keys, values))
//
#fetch value by key
d1['eggs']
//
#key membership test
>>> dict={'a':1,'b':2,'c':3}
>>> 'a' in dict
True
>>> 'd' in dict
False
>>> if not 'f' in D:
       print('missing')
//
#get the value for a specific key if it exists, if not it will assign
a default value:
>>> dict={'a':1,'b':2,'c':3}
>>> value=dict.get('c',0) #value will be 3
>>> value=dict.get('d',0) #value will be 0 because 'd' does not exist
//
#check if key exists in a 2 nested dictionary
d.get('key1',{}).get('key2')
//
#returns list with keys
>>> d1.keys()
['eggs', 'ham', 'spam']
//
#iterating through key/values simultaneously
>>>for k,v in d1.items():
>>>    print k,v
//
#another example of the use of a dict to organize the cities by state
>>> from collections import defaultdict
>>> city_list = [('TX','Austin'), ('TX','Houston'), ('NY','Albany'), ('NY', 'Syracuse'), ('NY', 'Buffalo'), ('NY', 'Rochester'), ('TX', 'Dallas'), ('CA','Sacramento'), ('CA', 'Palo Alto'), ('GA', 'Atlanta')]
>>>
>>> cities_by_state = defaultdict(list)
>>> for state, city in city_list:
...     cities_by_state[state].append(city)
...
for state, cities in cities_by_state.iteritems():
...     print state, ', '.join(cities)
...
NY Albany, Syracuse, Buffalo, Rochester
CA Sacramento, Palo Alto
GA Atlanta
TX Austin, Houston, Dallas
//
# better way of performing autovivification

class AutoVivification(dict):
    """Implementation of perl's autovivification feature."""
    def __getitem__(self, item):
        try:
            return dict.__getitem__(self, item)
        except KeyError:
            value = self[item] = type(self)()
            return value

a = AutoVivification()

a[1][2][3] = 4
a[1][3][3] = 5
a[1][2]['test'] = 6

print(a)
//
#creating a nested dictionary defining a priory the number of levels
and the final value:

from collections import defaultdict

def autovivify(levels=1, final=dict):
    return (defaultdict(final) if levels < 2 else
            defaultdict(lambda: autovivify(levels - 1, final)))

words = autovivify(3, list)
words["sam"][2012][5].append('a')
words["sam"][2012][5].append('b')

#or:
words = autovivify(5, int)
words["sam"][2012][5][25]["hello"] += 1
words["sue"][2012][5][24]["today"] += 1


//
#create nested dictionary(dictionary of dictionary)
>>>d1={}
>>>d1["key1"]={
>>> "keyA":0,
>>> "keyB":1,
>>> "keyC":2,
>>> }
//
#checking for the existence of a key in a dictionary:
 if key in d:
        d[key] += 1
    else:
        d[key] = 1
//
#print out results
>>>for key in d1.keys():
>>>    for key1 in d1[key]:
>>>        print key1
keyC
keyB
keyA
//
#accessing a nested dictionary
>>>print d1["key1"]["keyA"]
0
//
#autovivification in python
def rec_dd():
    return defaultdict(rec_dd)

>>> x = rec_dd()
>>> x['a']['b']['c']['d']
defaultdict(<function rec_dd at 0x7f0dcef81500>, {})
//
dict.items() #This method returns a list of tuple pairs.

dict = {'Name': 'Zara', 'Age': 7}

print "Value : %s" %  dict.items()

Value : [('Age', 7), ('Name', 'Zara')]
//
#deleteing a key from dict:
>>> dict={'a':1,
... 'b':2,
... 'c':3}
>>> del dict['a']
>>> dict
{'c': 3, 'b': 2}
//
#creating a dictionary from list with indices as keys
a = [51,27,13,56]
b = dict(enumerate(a))
print(b)

will produce:

{0: 51, 1: 27, 2: 13, 3: 56}
//
#defaultdict. A defaultdict works exactly like a normal dict, but it is initialized with a function (“default factory”) that takes no arguments and provides the default value for a nonexistent key.
>>> from collections import defaultdict
>>> ice_cream = defaultdict(lambda: 'Vanilla')
>>>
>>> ice_cream = defaultdict(lambda: 'Vanilla')
>>> ice_cream['Sarah'] = 'Chunky Monkey'
>>> ice_cream['Abdul'] = 'Butter Pecan'
>>> print ice_cream['Sarah']
Chunky Monkey
>>> print ice_cream['Joe']
Vanilla
>>>
/
#Implementing a counter with defaultdict
from collections import defaultdict

string="a a b b b a a a b b b"
letters=string.split()
letter_count=defaultdict(int); # default value of int is 0

for letter in letters:
    letter_count[letter] +=1 # increment element's value by 1
//
# is used for comments
//
v1="hola"
v2="caracola"
//
#initializing 2 variables at the same time
v1,v2=1,2
//
#        #
#debugger#
#        #
pdb script.py #run python debugger
p variable #print variable contents
n #next statement
b 2 #create a breakpoint at line 2
run #restart the debugger
//
#creating a breakpoint within a function that is in a class:
b VcfQC.run_CollectVariantCallingMetrics #it has to be set after being imported
//
print 'hello'
//
>>>print 1,2 #print adding a space between
1 2
//
print 1,2, #print without newline at end of text
//
>>>a="ccc"
>>>print a.upper()
CCC
//
L1=[2,3,4] #create list (array)
print L1[0] #printing element at index=0
//
L1[-2] #accessing element but counting from the right
//
L1[2:] #slicing a list (from index at 2 until the last index)
//
L1=["c","a","c","a"] #create list with strings
//
#indexing strings
>>>h="hola"
>>>print h[0]
h
or
>>>print h[0:2]
ho
//
a="hola"
print len(a) #print out length of a
//
#concatenate
a="cac"
b="otas"
print a+b
//
#string+int concatenation
>>>a=1
>>>b="hola"
>>>c=str(a)+b
1hola
#a second way of doing this concatenation would be to use backticks
>>>a=1
>>>b="hola"
>>>c=`a`+b
//
#print a string and an int
>>>a=1
>>>print "caramelos=",a
//
convert string into integer
start="1000"
end=str(start)+1
//
>>>L1=["c","a","c","a"]
>>>print','.join(L1)
c,a,c,a
//
#to replace characters in a string
newstringObject=stringObject.replace(old,new)
//
#removing whitespaces from a string
>>> s="     I am learning\tpython"
>>> s.replace(' ','')
'Iamlearning\tpython'
//
#removing all whitespaces and replacing by single /t
>>> s="hola   adios"
>>> re.sub('\s+','\t',s)
'hola\tadios'
//
#using regex when replacing
>>>s='100 NORTH 100'
>>>re.sub('^100','200',s)
>>>re
>>>'200 NORTH 100'
//
#delete a fragment of a string
import re
url = 'abcdc.com'
url = re.sub('\.com$', '', url)
//
#Referencing the stdout:
import sys

sys.stdout
//
#print argv passed to the script
import sys
print sys.argv
//
print 3 in [1,2,3] #check membership
'TRUE'
//
for x in [1,2,3]: print x #iterate list
//
#to iterate over a certain range(from,to,interval)
>>>for i in range(0,3,1):
>>>    print i
//
#iterave over a list
>>>list=[1,2,3,4,5]
>>>for i in range(len(list)):
...     print list[i]
1 2 3 4 5

//
# append integer to the beginning of a list
>>> a = 5
>>> li = [1, 2, 3]
>>> [a] + li  # Don't use 'list' as variable name.
[5, 1, 2, 3]
//
#append an elements into a list
list=[1,2,3]
list.append(4)
//
#append several elements onto list
list=[1,2,3]
list.extend([4,5,6])
//
#delete and print last element(item)
>>>list=[1,2,3]
>>>print list.pop()
3
//
#delement an element in the list
>>>list=[1,2,3]
>>>del list[0]
>>>print list
2,3
//
#reverse a list
list.reverse()
//
#using lists as stacks
#a stack is a data structure where the last element added is the first element retrieved("last-in,first-out"):
>>>stack=[3,4,5]
>>>stack.append(6)
>>>stack.append(7)
>>>>>> stack
[3, 4, 5, 6, 7]
>>> stack.pop()
7
>>> stack
[3, 4, 5, 6]
>>> stack.pop()
6
>>> stack.pop()
5
>>> stack
[3, 4]
//
#Using Lists as Queues
You can also use a list conveniently as a queue, where the first element added is the first element retrieved (“first-in, first-out”). To add an item to the back of the queue, use append(). To retrieve an item from the front of the queue, use pop() with 0 as the index. For example:
>>> queue = ["Eric", "John", "Michael"]
>>> queue.append("Terry")           # Terry arrives
>>> queue.append("Graham")          # Graham arrives
>>> queue.pop(0)
'Eric'
>>> queue.pop(0)
'John'
>>> queue
['Michael', 'Terry', 'Graham']
//
#create dictionary (hash)
d1={'spam':2,'ham':1,'eggs':3}
//
#fetch value by key
d1['eggs']
//
#key membership test
>>> d1.has_key('ham')
True
//
#returns list with keys
>>> d1.keys()
['eggs', 'ham', 'spam']
//
#iterating through key/values simultaneously
>>>for k,v in d1.items():
>>>    print k,v

//
#create nested dictionary(dictionary of dictionary)
>>>d1={}
>>>d1["key1"]={
>>> "keyA":0,
>>> "keyB":1,
>>> "keyC":2,
>>> }
#print out results
>>>for key in d1.keys():
>>>    for key1 in d1[key]:
>>>        print key1
keyC
keyB
keyA
//
#iterate over this is sorted order by the key
>>> steps = {1:"val1", 5:"val2", 2:"val3"}

>>> for key in sorted(steps):
...     print steps[key]
...
val1
val3
val2
//
#accessing a nested dictionary
>>>print d1["key1"]["keyA"]
0
//
#sorting a dictionary by its keys
def sortedDictValues(adict):
    keys = adict.keys( )
    keys.sort( )
    return [adict[key] for key in keys]
//
#In Python2.7, an OrderedDict can be used to sort a dictionary by its
keys:
sd = OrderedDict(sorted(d.items())) #where d is the dictionary to sort
//
#looping through a sorted dict:
python_words = {'list': 'A collection of values that are not connected, but have an order.',
                'dictionary': 'A collection of key-value pairs.',
                'function': 'A named set of instructions that defines a set of actions in Python.',
                }

for word in sorted(python_words.keys()):
    print(word)
//
#sorting a dictionary by its values
>>>d1={
>>>    'a':2,
>>>    'b':4,
>>>    'c':3,
>>>    'd':1
>>>    }
>>>
>>>sortedKeys=sorted(d1.items(), key=lambda(k,v):(v,k))
>>>
>>>for thisKey in sortedKeys:
>>>    print thisKey[0],d1[thisKey[0]]
d 1
a 2
c 3
b 4
//
#counting characters in a string
>>>string="aaabbb"
>>>charCount={}
>>>for char in string:
>>>  charCount[char]=charCount.get(char,0)+1
>>>print charCount
{'a': 3, 'b': 3}
//
myfile=open('myfile','w') #open for output (creates)
myfile.write('hello text file\n') #write a line of text
myfile.close()
//
>>> myfile=open('myfile','r') #open for input
>>> myfile.readline()	            #read the line back
'hello text file\n'
//
#open a file and throws an error if file does not exist
file="filename"

#check if file exists
if os.path.isfile(file) == False:
    raise Exception("File does not exist")

#getting the dir for a certain file:
dir=os.path.dirname(os.path.abspath(file))

#check if dir exists
import os

os.path.isdir('./dir')
//
#better way of opening a file (it closes the file when there is an error)
#using with
with open("x.txt") as f:
    data = f.read()
    do something with data
/
#or reading line per line
with open("x.txt") as f:
 for line in f:
       print line,
//
#os module
//
*get the file size of a certain file
import os
os.path.getsize('C:\\Python27\\Lib\\genericpath.py')
//
#getting the current working directory
>>>import os
>>> print os.getcwd()
/data/scratch/ernesto/454/SCD1/SNPs
//
#return all files in a directory as a list
>>>os.listdir(os.getcwd())
or
>>>os.listdir('.')
//
#getting extension of a file
>>>import os 
>>> os.path.splitext('caca.txt')
('caca', '.txt')
//
>>> filename='/Users/ernesto/projects/IGSR/files/testABC.pdf'
22>>> os.path.basename(filename).split('.')[0]
'testABC'
//
#splitting an absolute path in /path/ and file name
>>>import os
>>> os.path.split('/data/genomes/human36/chr1.fa')
('/data/genomes/human36/','chr1.fa')
//
#globbing or reading files from a directory
import glob
glob.glob("/data/scratch/ernesto/454/SCD1/againstGenes/snps/*txt")
//
#globbing
import glob
for file in glob.glob("*txt"):
    print file
/
# globbing and filtering the resulting files based on a pattern:
import glob
res = [f for f in glob.glob("*.txt") if "abc" in f or "123" in f or "a1b" in f]
for f in res:
    print(f)
//
#delete a file
os.remove('afile')
//
#renaming a file
os.rename(filename,newfilename)
//
#if statement
>>>x=2;
>>>if x==1:
>>>    print "hello"
>>>elif x==2:
>>>    print "caca"
>>>else:
>>>    print "cacotas"
//
#negating ifs
if not x==1:
   print "hello"
//
#while loop
>>>a=0; b=10
>>>
>>>while a<b:
>>>    print a,
>>>    a+=1
0 1 2 3 4 5 6 7 8 9
//
*args and **keywordargs for functions definitions are used for passing lists of arguments and dictionaries of arguments, respectively. So if I had a function this:

def printlist(*args):
    for x in args:
        print x

printlist(1, 2, 3, 4, 5) # or as many more arguments as I'd like

def printdict(**kwargs):
    print repr(kwargs)

printdict(john=10, jill=12, david=15)
//
#using a default value for an argument that can be passed through the
**kwargs dictionary

def printdict(a,b=5,**kwargs):
    print("b="+str(b))

printdict(a=1,john=10, d=12, david=15)
#will print b=5, but if b is passed, then the new value of b will be printed
//
#passing a dictionary to a function having **kwargs
def printdict(a,b=3,**kwargs):
    print("a="+str(a))
    print("b="+str(b))
    print repr(kwargs)


d={'john':1,'b':2,'david':3}
printdict(a=1,**d)
//
* setting class attributes dynamically with variable number of arguments and kwargs:
class Bar(object):
    def __init__(self, **kwargs):
        self.__dict__.update(kwargs)

bar = Bar(a=1, b=2)

print(bar.b)
/
* And if you want to allow only a certain attributes:
class Bar(object):
    def __init__(self, **kwargs):
        allowed_keys = ['a', 'b', 'c']
        self.__dict__.update((k, v) for k, v in kwargs.items() if k in allowed_keys)
//
#passing a dictionary to a function
def my_function(city, standard, name, school=None):
    schoolname  = school
    cityname = city
    standard = standard
    studentname = name
    print(cityname)


data = {'standard': '7', 'name': 'abc', 'city': 'delhi'}

my_function(**data)
//
#create times function
>>>def times(x,y):
>>>   return x*y
>>>product=times(2,4)
>>>print product
8
//
#in python lists,dictionaries and tuples are basic types. So they can be passed as arguments for functions
//
#checking the type of an object
>>>a=1
>>>type(a)
<type 'int'>
//
REGEX
\d matches any decimal digit, [0-9]
\D matches any non-digit character [^0-9]
\s matches any whitespace character [ \t\n\r\f\v]
\S matches any non-whitespace character [^ \t\n\r\f\v]
\w matches any alphanumeric character [a-zA-Z0-9_]
\W matches any non-alphanumeric character [^a-zA-Z0-9_]
//
Performing Matches:
match() #determine if the RE matches at the beginning of the string
search() #scan through a string, looking for any location where this RE matches
findall() #find all substrings where the RE matches, and returns them as a list
finditer() #find all substrings where the RE matches, and return them as an iterator
//
REGEX
>>>import re #module for regex
>>>p=re.comple('^>') #compile patternp
>>>print p.match("") #if match then returns a match object. if not then returns none
None
//
#open a file and splitting by newlines:
with open("out.txt") as f:
    data = f.read().splitlines()
    print "h\n"
//
#open a file a print out all lines starting with a pattern:
with open("test.fasta") as f:
   for line in f:
       if line.startswith(">"):
           print line,

//
#grouping in the REGEX
>>>dna="chr14:10000-20000"
>>>p=re.compile("(chr\d+):(\d+)-(\d+)")
>>>m=p.match(dna)
>>>print m.group(0) #returns the whole match
>>>chr=m.group(1)
>>>start=m.group(2)
>>>end=m.group(3)
>>>print chr
>>>print start
>>>print end
chr14:10000-20000
chr14
10000
20000
//
#matching 5 as
a{5}
//
#parsing a file and skipping lines starting with a certain pattern
import re
p=re.compile('^#') #compile pattern

infile=open('filename','r')
while 1:
       line=infile.readline()
       if p.match(line):continue
//
#Create a List that contain each Line of a File
List = open("filename.txt").readlines()
//
#Structure of an exception:
try:
   You do your operations here;
   ......................
except ExceptionI:
   If there is ExceptionI, then execute this block.
except ExceptionII:
   If there is ExceptionII, then execute this block.
   ......................
else:
   If there is no exception then execute this block. 

#Ex:
#!/usr/bin/python

try:
   fh = open("testfile", "w")
   fh.write("This is my test file for exception handling!!")
except IOError:
   print "Error: can\'t find file or read data"
else:
   print "Written content in the file successfully"
   fh.close()

//
#List comprehensions:

Everything that can be expressed as a 'for' loop can be expressed with a list comprehension. For example (with pseudocode):

new_things = []
for ITEM in old_things:
    if condition_based_on(ITEM):

Can be expressed:

new_things = ["something with " + ITEM for ITEM in old_things if condition_based_on(ITEM)]

With a real example:

numbers = [1, 2, 3, 4, 5]

doubled_odds = []
for n in numbers:
    if n % 2 == 1:
        doubled_odds.append(n * 2)

Can be transformed to:

numbers = [1, 2, 3, 4, 5]

doubled_odds = [n * 2 for n in numbers if n % 2 == 1]

#if the for loop does not have a condition. Then it is even simpler:
doubled_numbers = []
for n in numbers:
    doubled_numbers.append(n * 2)

Gets to:
doubled_numbers = [n * 2 for n in numbers]

#For nested loops (for example, if we want to flatten a matrix):

flattened = []
for row in matrix:
    for n in row:
        flattened.append(n)

Then the comprehension would be:

flattened = [n for row in matrix for n in row]
//
*Using regex on the elements of a list:
*Good explanation at:
http://www.cademuir.eu/blog/2011/10/20/python-searching-for-a-string-within-a-list-list-comprehension/
>>> import re
>>> list=['a cat','a dog','a yacht','cats']
>>> regex=re.compile(".*(cat).*")
>>> [m.group(0) for l in list for m in [regex.search(l)] if m]
['a cat', 'cats']
>>> [m.group(1) for l in list for m in [regex.search(l)] if m]
['cat', 'cat']
//
# catch all exceptions
try:
    ...
except:

# catch just one exception
try:
    ...
except IOError:
    ...

# catch one exception, but provide the exception object
try:
    ...
except IOError, e:
    ...

# catch more than one exception
try:
    ...
except (IOError, ValueError), e:
    ...
//
#raising exceptions, allows the programmer to force a specified exception to occur.
>>>try:
>>>	raise NameError('HiThere')
>>>except NameError:
>>>	  print 'An exception flew by!'
>>>	  raise
//
*TypeError exceptions:
:
*We are trying to access a string as it were a dict
a="abc"

try:
     value = a['a']
except TypeError,e:
    print "Not valid",e
#e will contain more info in the error cause

//
>>>a="hola,"
>>>print a.strip(",")
hola
//
#remove newline character in the right side
line=line.rstrip("\n")
//
#remove all spaces in the right side
line=line.rstrip()
//
#remove all spaces in any of the sides
line=line.strip()
//
while <test1>:
      <statements1>
      if<test2>: break #last equivalent
      if<test3>: continue
      if<test4>: pass
//
+= #concatenate operator
//
#or logical operator
if a=="a" or a=="b":
//
#and logical operator
if a=="a" and a=="b"
//
#increment operator
variable+=1
//
#map, executes passed in function over each item in a list
>>>def inc(x):return x+10
>>>L=map(inc,[1,2,3])
>>>print L
//
#list comprenhension (shortcut to create lists from other lists by specifying a formula to be applied to each element)
>>>[x*x for x in [1,2,3]]
[1, 4, 9]
/
*concat a string to all elements of a list using comprenhension
>>>['concat_'+x for x in ['a','b','c']]
['concat_a', 'concat_b', 'concat_c']
/
#another example:
pow2 = [2 ** x for x in range(10)]
//
#getting user input
name=(raw_input("Como te llamas?"))
//
#exceptions
//
#raising a IOError exception
try:
    f=open('normoxia_70bp.aln.nativ','r')
except IOError, e:
    print e
//
#casting to a int
a="1"
b=int(a)
//
#casting into a float
a="1.245"
b=float(a)
//
#string formatting
>>> exclamation="Ni"
>>> "The knights who say %s!" % exclamation
'The knights who say Ni!'
//
"%d %s %d you" % (1,'spam',4)
'1 spam 4 you'
//
*If one want to repeat the same string several times, instead of
doing:
s='arbit'
string='%s hello world %s hello world %s' %(s,s,s)

*It is better to use (available from  Python 2.6 and Python 3.x:):

incoming = 'arbit'
result = '{0} hello world {0} hello world {0}'.format(incoming)
//
#formatting a float (setting the number of decimal places)
>>> a=1.23456789
>>> '%.2f' % a
'1.23'
//
#Differences between %s and %r:
%s invokes str(), whereas %r invokes repr().
Ex:
 x = "example"
 print "My %s"%x

       My example

 print "My %r"%x

       My 'example'
//
#Another way, using string format method.
Printing out a table:
table={'hola': 1, 'adios':2, 'bye':3}

for name,phone in table.items():
  print '{0:10} ==> {1:40d}'.format(name,phone)

bye        ==>                                        3
hola       ==>                                        1
adios      ==>                                        2

10 and 40 controls the amount of spaces in each cell,
the d is because we are dealing with integers, if we would have
strings, we should use 40s
//
#Calling a function for each object within a list of objects (in this
case we invoke the mass function)
sumofmass = sum(i.mass for i in objList)
//
#exitting the script
sys.exit()
//
#making a python script executable
#!/usr/bin/python
print "KAKOTAS!!!"
#chmod +x prueba.py
//
#issue warnings to STDER
import warnings
warnings.warn("Hello")
//
#process management
>>>import subprocess
>>>
>>>subprocess.Popen(['/bin/echo','hola']) #open a process, args is a list in which list[0] is the command and list[>1] are the command arguments
#NOTE. If we open processes in a loop, this subprocess module allows
to open several processes concurrently. This functionality may crash
the server
/
#gettng the stdout and stderr
from subprocess import Popen, PIPE
cmd = 'blah'
p = Popen(cmd, stdout=PIPE, stderr=PIPE)
stdout, stderr = p.communicate()

/
#run ls and store its output
import subprocess
       ls_output = subprocess.check_output(['ls'])
#to pass args, #the first elem is the command name and the rest are
the args
subprocess.check_output(['ls', '-l'])
#
#this will not work, the shell considers the entire string as
something to be executed
subprocess.call(['ls -l'])
#
#this would work:
subprocess.call('ls -l', shell=True)
//
returncode=subprocess.call("ls -l", shell=True)
#if returncode=0 then everything went well, if not then it will 1
//
*running a process and accessing the error when something went wrong:
import subprocess

try:
    subprocess.check_output("ls -l",shell=True)
except subprocess.CalledProcessError as e:
    print(e.output)
//
#another way of opening subprocesses is os.system(). It is easier to use than subprocess but user do not have the same level of control over the subprocesses.
#If you have several arguments to be passed to the process, a List is not needed.The use of system is equivalent to Perl system()
#System only open one process at a time
>>>import os
>>>os.system("blat database file -minIdentity=100 -out=pslx
outputname.pslx")
//
#declaring and initializing several variables at a time
(a,b)=('a','b')
or
(a,b)=('','')
//
#sort a list
>>>array=[2,1,4,3,5,6]
>>>array.sort()
>>>print array
[1, 2, 3, 4, 5, 6]
//
#getting the index of a cetain element in an array
["foo", "bar", "baz"].index("bar")
1
//
>>>4%2 #modulus
//
#calculating median
array=[2,1,4,3,5,6]

array.sort()

count=len(array)

median=0.0
if count%2:
    #odd
    median=array[int(count/2)];
else:
    #even
    lower=float(array[(count/2)-1])
    upper=float(array[count/2])
    median=(float(array[count/2])+float(array[count/2-1]))/2
print median
//
#multiline printing
>>>print """
>>>First line.
>>>Second line.
>>>Third line.
>>>"""

First line.
Second line.
Third line.

//
#installing python eggs:
sudo easy_install JsonUtils
or
pip install python_module_name #this will install it in
/homes/ernesto/.local/lib/python2.7/site-packages/
/
#knowing where pip installs the modules:
>>> import site; site.getsitepackages()
/
#Changing the default install location for pip:
pip install --install-option="--prefix=/homes/ernesto/" packagename
/
#knowing list of installed packages and versions:
pip list
/
#If you have a program working in a given computer, then get a freeze
of all pip modules installed:
pip freeze > requeriments.txt

#then, install all modules required on a new computer using:
pip install -r requirements.txt
/
#upgrade a given package:
pip install modulename --upgrade
/
#uninstall a package:
pip uninstall packagename
/
#installing easy_install locally:
wget https://bootstrap.pypa.io/ez_setup.py -O - | python - --user
#will install it at:
/homes/ernesto/.local/bin/
/
#using easy_install for installing in a given dir:
~/.local/bin/easy_install-2.7 --install-dir /homes/ernesto/.local/lib/python2.7/site-packages pip
/
*If pip it is not installed, you will need to install it by doing:
sudo easy_install pip
//
#installing package from source
#use the option --record files.txt to know what files were created
python setup.py  install --record files.txt --home=/nfs/research2/flicek/user/ernesto/
//
#knowing the location of an installed package:
pip show packagename
//
#classes in Python
#!/usr/bin/python

class Employee:
   'Common base class for all employees'
   empCount = 0

   def __init__(self, name, salary):
      self.name = name
      self.salary = salary
      Employee.empCount += 1
   
   def displayCount(self):
     print "Total Employee %d" % Employee.empCount

   def displayEmployee(self):
      print "Name : ", self.name,  ", Salary: ", self.salary

"This would create first object of Employee class"
emp1 = Employee("Zara", 2000)
"This would create second object of Employee class"
emp2 = Employee("Manni", 5000)
emp1.displayEmployee()
emp2.displayEmployee()
print "Total Employee %d" % Employee.empCount
//
#reading in a Json file
import json
from pprint import pprint

file=open('test.json','r')

parsed_json = json.load(file)

pprint(parsed_json)
//
*Creating your own module:
Read tutorial at:
http://www.tutorialspoint.com/python/python_modules.htm
//
*Creating your own package:
Read at tutorial at:
http://www.tutorialspoint.com/python/python_modules.htm
//
*The dir() function:
The dir() built-in function returns a sorted list of strings
containing the names defined by a module.

For example:
# Import built-in module math
import math

content = dir(math)

print content

//
*Parsing XML
One useful module is xmltodict. Read on it at:
http://docs.python-guide.org/en/latest/scenarios/xml/
/
#parsing and writing out a xml file:
with open('analysis.xml') as fd:
    doc = xmltodict.parse(fd.read())
    doc['ANALYSIS_SET']['ANALYSIS']['ANALYSIS_TYPE']['REFERENCE_ALIGNMENT']['ASSEMBLY']['STANDARD']['@refname']="GRCh37"
    print (xmltodict.unparse(doc,encoding='utf-8',pretty=True))
#Problem is that is not respect the element order when unparsing
//
*Counter in Python:
>>> from collections import Counter
>>> Counter(['apple','red','apple','red','red','pear'])
Counter({'red': 3, 'apple': 2, 'pear': 1})
//
#creating datetime objects:
>>> import datetime
>>>
>>> x = datetime.datetime(2020, 5, 17)
>>> print(x)
2020-05-17 00:00:00
/
#or :
>>> x = datetime.datetime(2020, 5, 17,22,30)
>>> print(x)
2020-05-17 22:30:00
//
*Working with dates:

from datetime import datetime

now = datetime.now()
print "Now: ", now
print "Today's date: ", now.strftime('%Y-%m-%d') 

print "year:", now.year
print "month:", now.month
print "day:", now.day
print "hour:", now.hour
print "minute:", now.minute
print "second:", now.second
/
*Converting strings to dates:
from datetime import datetime

datetime_object = datetime.strptime('Jun 1 2005  1:33PM', '%b %d %Y
%I:%M%p')

candle = datetime.strptime("2015-10-24 21:10:05", "%Y-%m-%d %H:%M:%S")
/
*datetime in isoformat
print datetime.isoformat()
2015-10-19T21:00:00
/
*Convert string into datetime
from datetime import datetime

date_object = datetime.strptime('Jun 1 2005  1:33PM', '%b %d %Y
%I:%M%p')
/
#dates arithmetics:
import datetime

d=datetime.datetime.strptime("2016-10-26", "%Y-%m-%d").date()

one_day = datetime.timedelta(days=3) 

yesterday = d - one_day

print yesterday
/
* Getting hours, hours, days from timedelta
>>> import datetime
>>> x = datetime.datetime(2020, 5, 17,22,30)
>>> y = datetime.datetime(2020, 5, 16,22,30)
>>> d= x-y
>>> d.days
Returns 2 (days in this case)

If the timedelta is not a whole, then we will get 
seconds that we will need to convert to hours
>>> x = datetime.datetime(2020, 5, 17,22,30)
>>> y = datetime.datetime(2020, 5, 16,23,00)
>>> d= x-y
>>> d.days
0
>>> d.seconds
84600
>>> d.seconds/3600
In hours


/
*another way of dealing with dates:
/
*Adding single days:
import pandas as pd

ic="2016-12-11 22:00:00"
D=pd.DateOffset(1)

# pd.datetime is an alias for datetime.datetime
candle = pd.datetime.strptime(ic, "%Y-%m-%d %H:%M:%S")
start=candle-2*D
end=candle+2*D
//
*Knowing the weekday:
datetime.datetime.today().weekday()
//
*substracting 2 times (differences between 2 dates):
# Create datetime objects for each time (a and b)
dateTimeA = datetime.datetime.combine(datetime.date.today(), a)
dateTimeB = datetime.datetime.combine(datetime.date.today(), b)
# Get the difference between datetimes (as timedelta)
dateTimeDifference = dateTimeA - dateTimeB
# Divide difference in seconds by number of seconds in hour (3600)  
dateTimeDifferenceInHours = dateTimeDifference.total_seconds() / 3600
//
import pandas as pd
# BDay is business day, not birthday...
from pandas.tseries.offsets import BDay

# pd.datetime is an alias for datetime.datetime
today = pd.datetime.today()
print today - BDay(4)
/
* creating times
from datetime import time

# time(hour = 0, minute = 0, second = 0)
a = time()
print("a =", a)

# time(hour, minute and second)
b = time(11, 34, 56)
print("b =", b)

# time(hour, minute and second)
c = time(hour = 11, minute = 34, second = 56)
print("c =", c)

# time(hour, minute, second, microsecond)
d = time(11, 34, 56, 234566)
print("d =", d)
/
*Creating dates/times ranges:
*Hourly
import pandas as pd

ic="2016-12-11 22:00:00"

rng = pd.date_range('1/1/2011', periods=72, freq='H')

print rng[:5]
/
*Iterating over time_ranges:
for d in pd.date_range(start='2016-12-09',end='2016-12-15'):
    print d
//
*Initializing a time object with 0:00:00
import datetime

t = datetime.time(0, 0, 0) * (hours,minutes,seconds)
//
*getting the current time and date:
now = datetime.datetime.now()
/
#comparing 2 times:
import datetime

d.time()<datetime.time(22, 0, 0))
//
#comparing 2 dates:
if object.date()==datetime.date(2016,12,26):
//
#comparing 2 dicts in python 3:
d_1 = {'peter': 1, 'adam': 2, 'david': 3}
d_3 = {'peter': 1, 'adam': 2, 'david': 5}

print(set(d_1.keys()) == set(d_3.keys()))
print(set(d_1.values()) == set(d_3.values()))

//
*Connecting to mysql from Python.
Good tutorial at: 
https://www.tutorialspoint.com/python/python_database_access.htm
/
#SELECT query:

import datetime
import mysql.connector

cnx = mysql.connector.connect(user='scott', database='employees')
cursor = cnx.cursor()

query = ("SELECT first_name, last_name, hire_date FROM employees "
         "WHERE hire_date BETWEEN %s AND %s")

hire_start = datetime.date(1999, 1, 1)
hire_end = datetime.date(1999, 12, 31)

cursor.execute(query, (hire_start, hire_end))

#to know how many results the query returned, use:
res_count=cursor.rowcount

for (first_name, last_name, hire_date) in cursor:
  print("{}, {} was hired on {:%d %b %Y}".format(
    last_name, first_name, hire_date))

cursor.close()
cnx.close()

#getting the results from db:
data = cursor.fetchall() #returns an array of arrays
for row in data :
    do stuff
/
#another way (less typing):
other_ids = [row[0] for row in cursor.fetchall()]
/
PyMySQL
/
#getting results as a dictionary:
cursor = conn.cursor(MySQLdb.cursors.DictCursor)
cursor.execute("SELECT name, category FROM animal")
result_set = cursor.fetchall()
for row in result_set:
    print "%s, %s" % (row["name"], row["category"])
/
#connect mysql:
db =
MySQLdb.connect(host="mysql-g1kdcc-public",user="g1krw",passwd=????,port=4197,db="g1k_archive_staging_track"
)

#SQL statement:
db = MySQLdb.connect(host=args.host,user=args.user,passwd=args.pwd,port=args.port,db=args.db )

cursor = db.cursor()

sql_string="INSERT INTO file (file_id, name, md5,type,size,host_id,withdrawn,created) VALUES (NULL, '%s', '%s', '%s', %d,1,0,NOW())" % (path,md5sum,args.file_type,size)
try:
# Execute the SQL command
          cursor.execute(sql_string)
          # Commit your changes in the database
          db.commit()
     except MySQLdb.Error,e:
          print e[0], e[1]
          # Rollback in case there is any error
          db.rollback()

* If you want to get the id of the last inserted row, use:
cursor.lastrowid()

* If exception, then print the actual query used:
cursor._last_executed 
//
#parsing a sam file:
import pysam
samfile = pysam.AlignmentFile("ex1.bam", "rb")

for read in samfile.fetch('chr1', 100, 120):
     print read

samfile.close()
//
#getting the size of a file
import os

os.path.getsize(path)
//
#assert function
test a condition, and trigger an error if the condition is false.

For example:
i=5
assert i>2
#will no raise anything,

But if we do:

i=1
assert i>2

We get:
Traceback (most recent call last):
  File "test.py", line 3, in <module>
    assert i>2
AssertionError
//
#assert on a single line for testing a condition
>>> a=2
>>> assert a==1, "a variable is not 1"
//
# assert a datetime:

assert slist.start() == datetime.datetime(2019, 3, 10, 21, 0)

//
#knowing the environment within a function an outside the function:

a_global="hole"

def foo():
    print locals()

print foo()
print globals()
#And the output you get:
{}
None
{'a_global': 'hole', '__builtins__': <module '__builtin__'
(built-in)>, '__file__': 'test.py', '__package__': None, '__name__':
'__main__', 'foo': <function foo at 0x10e60a320>, '__doc__': None}

Whichs that the local environment within foo() is empty and the
global environment contains the variable declared that is named
'a_global'
//
#modifying the contents of PATH to a certain value
dict(os.environ,PATH="/homes/ernesto/lib")
//
#passing the desired PYTHONPATH at runtime:
PYTHONPATH=/path/to/ python script.py
//
*duck typing:
he idea is that it doesn't actually matter what type my data is - just
whether or not I can do what I want with it.
//
*In Python, everything is an object.
So strings can be used as arrays, because strings are objects that
contain the __get_item__ function

str="abc"
print str[0]   *will print a
print str[1]   * will print b
//
#Parameter checking in Python:
   1   from types import *
   2   class MyDB:
   3     ...
   4     def add(self, id, name):
   5       assert type(id) is IntType, "id is not an integer: %r" % id
   6       assert type(name) is StringType, "name is not a string: %r"
   % name

#Check if something is a list or a string:
#In Python3:
lst=[1,2,3]
assert not isinstance(lst, str)

#In Python2
assert not isinstance(lst, basestring)
//
# Check if something is either a float or int
a='s'

if not isinstance(a, (int, float)):
    print("a is either int or float")
//
#checking if something is a list:
if not isinstance(objs,list):
       print "h"
//
#checking if something is a number

import numbers

isinstance('a', numbers.Number)
>>> False
//
*merging (concatenate) 2 lists:
>>> a=[1,2,3,4]
>>> b=[2,3,4,5]
>>> a+b
[1, 2, 3, 4, 2, 3, 4, 5]
//
*zip It is a built-in function to merge together 2 lists in the
 following way:
 >>> names = ['Bob','Jessica','Mary','John','Mel']
>>> births = [968, 155, 77, 578, 973]

>>>> zip(names,births)
[('Bob', 968), ('Jessica', 155), ('Mary', 77), ('John', 578), ('Mel',
973)]
//
*Pandas: It is a module used for data analysis.
/
*First, creating a data.frame from a certain list:
from pandas import DataFrame, read_csv
/
*Panda's data structures:

**Series:
One-dimensional labeled array capable of holding any data
type(integers,strings, objects, etc.)

* iterating over Series:
for i, value in df['column'].mean().iteritems():
    print(i, value)

*Initializing:
s = pd.Series(data, index=index)

data can be:
a Python dict
an ndarray
a scalar value (like 5)

*Initializing from an ndarray:
s = pd.Series(np.random.randn(5), index=['a', 'b', 'c', 'd', 'e'])

*Initializing from a dict:
d = {'a' : 0., 'b' : 1., 'c' : 2.}
pd.Series(d)

//
#initialize dict with keys,values from two lists
keys = ['a','b','c','d']
values = [1,2,3,4]

d = dict(zip(keys, values))
//

*Accessing elements:
d['a']

*Operations on series:
In [43]: s[s>1]
c    2.0
dtype: float64

In [43]: s.mean()
Out[43]: 1.0

*They behave like dicts:
s.keys()

*Getting unique values from panda series:
s.unique()

//
*removing characters from strings in a list
lst = [("aaaa8"),("bb8"),("ccc8"),("dddddd8")]
print([s.strip('8') for s in lst]) # remove the 8 from the string borders
print([s.replace('8', '') for s in lst]) # remove all the 8s 

//
* Useful snippets on dataframes:
https://jeffdelaney.me/blog/useful-snippets-in-pandas/
//
# creating a random dataframe
df = pandas.DataFrame(np.random.randn(5, 3), columns=['a', 'b', 'c'])
//
* exploring the dataframe
df.shape        # number of rows/columns in a tuple

//
#creating a dataframe from numpy arrays:

data = np.array([['','Col1','Col2'],
                ['Row1',1,2],
                ['Row2',3,4]])
                
print(pd.DataFrame(data=data[1:,1:],
                  index=data[1:,0],
                  columns=data[0,1:]))

And this will produce:

<script.py> output:
         Col1 Col2
    Row1    1    2
    Row2    3    4
//
* using apply to apply a function over the column of a dataframe:
df['A']=df['A'].apply(lambda x:x+1)
//
* Filter a dataframe based on the outcome of a function applyied on a certain column
In [3]: df = pandas.DataFrame(np.random.randn(5, 3), columns=['a', 'b', 'c'])

In [4]: df
Out[4]: 
          a         b         c
0 -0.001968 -1.877945 -1.515674
1 -0.540628  0.793913 -0.983315
2 -1.313574  1.946410  0.826350
3  0.015763 -0.267860 -2.228350
4  0.563111  1.195459  0.343168

In [6]: df[df.apply(lambda x: x['b'] > x['c'], axis=1)]
Out[6]: 
          a         b         c
1 -0.540628  0.793913 -0.983315
2 -1.313574  1.946410  0.826350
3  0.015763 -0.267860 -2.228350
4  0.563111  1.195459  0.343168
//
* Difference between map, apply and applymap
Map: It iterates over each element of a series. 
df[‘column1’].map(lambda x: 10+x), this will add 10 to each element of column1.
df[‘column2’].map(lambda x: ‘AV’+x), this will concatenate “AV“ at the beginning of each element of column2 (column format is string).

Apply: As the name suggests, applies a function along any axis of the DataFrame.
df[[‘column1’,’column2’]].apply(sum), it will returns the sum of all the values of column1 and column2.

ApplyMap: This helps to apply a function to each element of dataframe.
func = lambda x: x+2
df.applymap(func), it will add 2 to each element of dataframe (all columns of dataframe must be numeric type)
//
# The inital set of baby names and bith rates
names = ['Bob','Jessica','Mary','John','Mel']
births = [968, 155, 77, 578, 973]

BabyDataSet = list(zip(names,births))

df = DataFrame(data = BabyDataSet, columns=['Names', 'Births'])

#selecting the first column of a dataframe:
df[[0]]

*adding a new columen to a dataframe
df['newcol']=toadd

*peeking the dataframe:
df.head()

*Getting a basic summary on a quantitative variable:
df['births'].describe()

*Getting the sum of a column:
Total = df['MyColumn'].sum()
print (Total)
319

*Getting the mean of a column:
df['births'].mean()

*Median
df['births'].median()

*10th percentile
df['births'].quantile(0.1)

*90th percentile
df['births'].quantile(0.9)

# Now, export the data.frame to a csv file
df.to_csv('births1880.csv',index=False,header=False)

# read-in the data frame from csv file:
df=read_csv('/Users/ernesto/Google_Drive/PYTHON_LEARN/births1880.csv')

# read-in the data frame from csv file specifying that the first row is the header
df=read_csv('/Users/ernesto/Google_Drive/PYTHON_LEARN/births1880.csv',heder=1)

# read-in the data.frame from csv file adding column names, and
  therefore an index
  df=read_csv('/Users/ernesto/Google_Drive/PYTHON_LEARN/births1880.csv',names=['col1','col2','col3'])

# read-in the data frame from tsv file:
df=pd.DataFrame.from_csv('/Users/ernesto/projects/IGSR/16_12_16/cov_DF.txt', sep='\t')

#read-in the data frame from file and skipping comments:
df = pd.read_csv("DF.txt",comment='#')

#read-in the data frame and specifying that 2 columns are dates
df = pd.read_csv('pizza.csv', parse_dates=['dates'])

#read-in the data frame and use only some columns
df = pd.read_csv('pizza.csv', usecols=['foo', 'bar'])

#  if first column is not picked, try with index_col=False
DF=pd.DataFrame.from_csv('/Users/ernesto/projects/IGSR/16_12_16/cov_DF.txt', sep='\t',index_col=False)

#read in the data frame without header
df=read_csv('/Users/ernesto/Google_Drive/PYTHON_LEARN/births1880.csv',header=None)

#knowing the data types in a dataframe
df.dtypes

#checking if a data.frame is empty:
if df.empty:
   do something

#checking if a list is empty:
if not a:
  print("List is empty")

#renaming column names in pandas data.frame:
df.columns = ['a', 'b']

#pretty print a data.frame
from tabulate import tabulate
import pandas as pd

df = pd.DataFrame({'col_two' : [0.0001, 1e-005 , 1e-006, 1e-007],
                   'column_3' : ['ABCD', 'ABCD', 'long string',
                   'ABCD']})
		   
print tabulate(df, headers='keys', tablefmt='psql')

+----+-----------+-------------+
|	  |   col_two         | column_3          |
|----+-----------+-------------|
|  0 |    0.0001 | ABCD        |
|  1 |    1e-05  | ABCD        |
|  2 |    1e-06  | long string |
|  3 |    1e-07  | ABCD        |
+----+-----------+-------------+

#copy a data.frame
surveys_copy = surveys_df.copy()

#slice a data.frame via indexes:
surveys_df.iloc[0:3, 1:4] #select 3 first rows and columns 1 to 4

#slice the first 2 columns and all the rows:
surveys_df.iloc[:, 1:4]

#accessing a cell
surveys_df.iloc[1, 2]

#slice and select different non-consecutive columns
surveys_df.iloc[:, [0,1,4]]

#accessing the actual value for a certain cell i
p df['colname'].item()

#iterating over a data.frame
for index, row in data1.iterrows():
    print(row['col1'])

#changing the data types within a dataframe
df=df.astype(int)

>>> df
         0    1
0      Bob  968
1  Jessica  155
2     Mary   77
3     John  578
4      Mel  973

#to select rows whose column value equals a scalar, some_value, use ==:
df.loc[df['column_name'] == some_value]

#to select applying more than one condition:
df1 = df.loc[(df.a != -1) & (df.b != -1)]

#selecting all rows that null values for a certain column:
df.loc[df['colname'].isnull()]

#Getting the columns names from a data.frame:
DF.columns

And the we access the first column:
df[0]
# printing the 3 first rows of the data frame
df[:3]

# Selecting by more than 1 column:
df[['col1',col2']]

*counting the values of one column if the variable is categorical:
df['col1'].value_counts()
/
#filling the NA values in a dataframe
DF.fillna(value=0)
/
#plotting a data.frame, one column versus the other:
 df.plot(x='col1',y='col2')
/
#getting the rownames of a dataframe in list format:
list(df.index)
/
#drawing a barplot
df.plot(kind='bar')
/
# Applying a function over a dataframe, see tutorial:
https://chrisalbon.com/python/pandas_apply_operations_to_dataframes.html
/
*Counting the occurrences of one variable by the occurrence of other,
(similar to R's table function):

print pd.crosstab(df['admit'], df['prestige'], rownames=['admit'])

prestige   1   2   3   4
admit                   
0         28  97  93  55
1         33  54  28  12
/
*With only one column:
pd.crosstab(index=df['instrument'], columns="count")
col_0       count
instrument       
AUD_USD        33
EUR_USD        35
USD_CAD        14
/
*How to make a pandas crosstab with percentages?
pd.crosstab(df.A, df.B).apply(lambda r: r/r.sum(), axis=1)
/
#crosstab plus plot
carat_table = pd.crosstab(index=diamonds["clarity"], columns="count")
carat_table.plot(kind="bar",
                 figsize=(8,8))
/
*Return evenly spaced numbers over a specified interval
from numpy import linspace

x = linspace(-5,5,100)
/
*Pandas conditional creation of a dataframe based on the value of one
column

import pandas as pd
import numpy as np

df=pd.DataFrame({'Type':list('ABBC'), 'Set':list('ZZXY')})
df['color']=np.where(df['Set']=='Z', 'green', 'red')
print(df)
/
import numpy as np

normally_distributed = np.random.normal(size=10000)  # Generate normal data*
/
*Pandas Dataframe columns are a Pandas Series when you pull them out,
which you can then call .tolist() on to turn them into a python list
dfList = df['one'].tolist()
/
#preventing poping windows when plotting:
import matplotlib
matplotlib.use("Agg")
import matplotlib.pyplot as plt
/
#creating a boxplot from quantitative variable using matplotlib:
import matplotlib.pyplot as plt
import numpy as np

# basic plot
plt.boxplot(data, labels=['set1','set2'])
#labels=adding labels to each set

/
#saving boxplot to file
import matplotlib.pyplot as plt
import numpy as np

# basic plot
plt.boxplot(data)

plt.savefig('/Users/ernesto/projects/IGSR/18_01_17/asdf.pdf',format='pdf')
/
#setting the axis labels and title
plt.xlabel("x axis", size=14) #and size also
plt.ylabel("y axis")
plt.title("caca", size=20)
/
#setting the size of the tick labels:
plt.tick_params(labelsize=20)
/
#creating a boxplot from a data.frame
df.boxplot()
/
# calculating the IQR (interquartile range) and whiskers and median in a boxplot

import numpy as np
import matplotlib.pyplot as plt

%matplotlib inline

data = np.random.rand(100)
plt.boxplot(data)

median = np.median(data)
upper_quartile = np.percentile(data, 75)
lower_quartile = np.percentile(data, 25)

iqr = upper_quartile - lower_quartile
upper_whisker = data[data<=upper_quartile+1.5*iqr].max()
lower_whisker = data[data>=lower_quartile-1.5*iqr].min()

/
* plotting a categorical variable (x variable) against a dependent variable (y variable):
See:
https://seaborn.pydata.org/tutorial/categorical.html
/
#rotating the X-labels:
df.plot(rot=90)
/
#changing the aspect of a boxplot
props = dict(boxes="DarkGreen", whiskers="DarkOrange", medians="DarkBlue", caps="Gray")

ax=df.plot.box(grid=True,return_type='axes',color=props, patch_artist=True)
/
#setting the color
df.plot(kind='bar',color="red")
/
#applying an y limit
df.plot(ylim=[0,50])
//
#setting the figure size
df.plot(figsize=[10,10])
//
#creating a plot from dataframe and saving
ax = df.plot()
fig = ax.get_figure()
fig.savefig('asdf.png')
fig.savefig('/Users/ernesto/projects/IGSR/files/asdf.pdf',format='pdf')
#saving in pdf format
/
Setting the xticks labels:
ax=subDF.plot()
ax.set_xticklabels(['a','b','c'])
/
#reducing the number of x axis ticks and labels to a certain frequency (setting only
every n tick)

n = 10

ax = df.plot()
ticks = ax.xaxis.get_ticklocs()
ticklabels = [l.get_text() for l in ax.xaxis.get_ticklabels()]
ax.xaxis.set_ticks(ticks[::n])
ax.xaxis.set_ticklabels(ticklabels[::n])

ax.figure.show()
//
*How to display all label values
ax=DF.plot()
ax.set_xticks(np.arange(len(DF.index)))
ax.set_xticklabels(DF.index)
//
*Creating a composed plot
import matplotlib.pyplot as plt
plt.figure(1)                # the first figure
plt.subplot(311)             # the first subplot in the first figure
plt.plot([1, 2, 3])
plt.subplot(312)             # the second subplot in the first figure
			       	   	 in a new row
plt.plot([4, 5, 6])
plt.subplot(313)             # the third subplot in the first figure
			       	   	 in a new row
plt.plot([7, 8, 9])

*Where subplot(3,1,3) is nrow,ncol,fignum. The maximum value in fignum
will depend on nrow*ncol
//
#useful reading on groupby and applying operations on gropus:
https://chrisalbon.com/python/data_wrangling/pandas_apply_operations_to_groups/
//
*Group data in the DataFrame by a certain column:
bytreatment = data.groupby('Treatment')

*Then, print descriptive stats for each of the values in Treatment:
>>>bytreatment['RelativeFitness'].describe()
Treatment       
Dish       count    32.000000
           mean      1.456359
           std       0.184792
           min       0.955221
           25%       1.429005
           50%       1.510884
           75%       1.581340
           max       1.699276
Tube       count    32.000000
           mean      0.929589
           std       0.050153
           min       0.795107
           25%       0.915050
           50%       0.939089
           75%       0.953505
           max       1.000363
dtype: float64
/
*Mean for each group:
>>>bytreatment['RelativeFitness'].mean()
Treatment
Dish    1.456359
Tube    0.929589
Name: RelativeFitness, dtype: float64
/
*Aggregating and applying different numpy functions:
bytreatment['RelativeFitness'].agg([np.mean,np.std,len,np.sum])
/
*Print a groupby dataframe:
import pandas as pd
df = pd.DataFrame({'A': ['one', 'one', 'two', 'three', 'three', 'one'], 'B': range(6)})

grouped_df = df.groupby('A')

for key, item in grouped_df:
    print(grouped_df.get_group(key))

//
* Plotting with matplotlib
import numpy as np
import matplotlib.pyplot as plt

*create an array
x=np.linspace(0,5,10)
y=x*x

fig,ax=plt.subplots()
ax.plot(x,y)

plt.show()
//
#NumPY:

#Create a NumPy array:
import numpy as np
import pandas as pd

data=np.array([['','Col1','Col2'],['Row1',1,2],['Row2',3,4]])

>>>data[1:,] #print from row 1 till the end:
array([['Row1', '1', '2'],
       ['Row2', '3', '4']],
      dtype='|S4')
>>>data[1,1]
'1'
//
#readin a np array from file:
good_set=np.fromfile("file.txt",dtype=float,sep="\n")
//
#calculating the mean on a numpy array:
np.mean(array)
//
#checking if elements within array are greater than some value
np.where(data>10)
//
# Transforming a dataset (logarithmic)
np.log(data)
//
# Transforming a dataset (square root)
np.sqrt(data)
//
#calculating max and min in an array:
np.amax(data)
np.amin(data)
//
#converting a numpy array to list:
data.tolist()
//
#How to append elements to a numpy array
A = np.array([])
for row in matrix:
    A = numpy.append(A, row)
//
#creating now a DataFrame from the Numpy array,
df=pd.DataFrame(data=data[1:,1:],index=data[1:,0],columns=data[0,1:])
//
#Using Jupyter.
If you want to use inline matplotlib plots in this platform, use:
%matplotlib inline
//
#selecting several cells
shift+j
//
#create virtual environment for a project:
cd my_project_folder
$ virtualenv venv #where venv is the virtual env name

#then, start using it:
source venv/bin/activate

#when you are done:
deactivate

#once the env is active, to list the modules that are local (in the
 env) only:
 pip list --local

#Anaconda:

#To install a package
conda install packagename

#To install a package from a certain channel
conda install -c bioconda pybedtools

#We can upgrage packages:

conda update numpy

#Verify environment we are right now:
conda info --envs

#create a new environment with some packages installed
conda create --name bamqc numpy pandas

#activate the created environment
source activate bamqc

#deactivate the environment
source deactivate

#installing a new environment with a new python version:
conda create --name blahblah python=2.7

#installing a new version with all python packages included in anaconda
conda create -n python2.7_env python=2.7 anaconda

#list all envs
conda env list

#remove a given env
conda remove --name bamqc --all
//
#correcting indentation errors, use python ~/bin/Python-2.7.12/Tools/scripts/reindent.py
//
# round all elements in a list
alist = [0.30000000000000004, 0.5, 0.20000000000000001]
my_rounded_list = [ round(elem, 2) for elem in alist ]

Will return:
[0.3, 0.5, 0.2]
//
#rounding to the nearest 10:
import math

def roundup(x):
    return int(math.ceil(x / 10.0)) * 10

# iterating through object attributes:
for attr, value in anobject.__dict__.iteritems():
        print attr, value

#ternary operator
value_when_true if condition else value_when_false

#For example:
'Yes' if fruit == 'Apple' else 'No'

*Enumerations in Python:

>>> from enum import Enum
>>> class Color(Enum):
...     red = 1
...     green = 2
...     blue = 3
...
*Enumeration members have human readable string representations:
>>> print(Color.red)
Color.red

*Enum members also have a property that contains just their item name:
>>> print(Color.red.name)
red

*Enumerations support iteration, in definition order:
>>> class Shake(Enum):
...     vanilla = 7
...     chocolate = 4
...     cookies = 9
...     mint = 3
...
>>> for shake in Shake:
...     print(shake)
...
Shake.vanilla
Shake.chocolate
Shake.cookies
Shake.mint

Enumeration members are hashable, so they can be used in dictionaries and sets:

>>> apples = {}
>>> apples[Color.red] = 'red delicious'
>>> apples[Color.green] = 'granny smith'
>>> apples == {Color.red: 'red delicious', Color.green: 'granny smith'}
True
//
#grep on the elements of a list:
>>> names = ['aet2000','ppt2000', 'aet2001', 'ppt2001']
>>> filter(lambda x:'aet' in x, names)
['aet2000', 'aet2001'] # in python 2,
#In python 3:
list(filter(lambda x:'aet' in x, names))
//
#function to check if a string represents a number:
def is_number(s):
    try:
        float(s)
        return True
    except ValueError:
        return False
//
#Creating an iterator object

class Fib:                                        ①
    def __init__(self, max):                      ②
        self.max = max

    def __iter__(self):                           ③
        self.a = 0
        self.b = 1
        return self

    def __next__(self):                           ④
        fib = self.a
        if fib > self.max:
            raise StopIteration                   ⑤
        self.a, self.b = self.b, self.a + self.b
        return fib        class Fib:                                        ①
    def __init__(self, max):                      ②
        self.max = max

    def __iter__(self):                           ③
        self.a = 0
        self.b = 1
        return self

    def __next__(self):                           ④
        fib = self.a
        if fib > self.max:
            raise StopIteration                   ⑤
        self.a, self.b = self.b, self.a + self.b
        return fib

>>> from fibonacci2 import Fib
>>> for n in Fib(1000):
...     print(n, end=' ')
0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987
//
*Containers in python:
Containers are any object that holds an arbitrary number of other objects. Generally, containers provide a way to access the contained objects and to iterate over them.

Examples of containers include tuple, list, set, dict; these are the built-in containers. More container types are available in the collections module.
//
*Getting the absolute number of a number
abs(a)
//
#glob in python
>>> import glob
>>> glob.glob('*.pl')
or :
>>> glob.glob("/path/to/file/TSI*")
//
#glob and sort
for file in sorted(glob.glob("*.fastq*")):
    print(file)
//
#iterating over 2 lists at the same time:
a=[1,2,3]
b=[2,4,6]

for i, j in zip(a, b):
    print(i,j)
//
#opening a gzipped file:
import gzip

with gzip.open('ALL.chip.omni_broad_sanger_combined.20140818.snps.genotypes.hg38.autosomes.maf0.01_call_rate_0.95.recoded.vcf.gz','r') as fin:
    for line in fin:
        print('got line', line)
#in this case, the line returned is in bytes format

#opening now and returning a text:
with gzip.open(sys.argv[1], 'rt') as f:
    for line in f:
        if line.startswith(b"#CHROM"):
            print(line)
#note that #CHROM is opened as a bytes stream and not a string, so
this is why wee need this 'b'
/
#converting a bytes object into str:
>>> b"abcde"
b'abcde'

# utf-8 is used here because it is a very common encoding, but you
# need to use the encoding your data is actually in.
>>> b"abcde".decode("utf-8") 
'abcde'
/
#encoding to bytes a certain str
b = mystring.encode('utf-8')
/
#create a compressed gzip file
import gzip
content = "Lots of content here"
with gzip.open('file.txt.gz', 'wb') as f:
    f.write(content)
//
#logging:
A good tutorial at http://www.blog.pythonlibrary.org/2012/08/02/python-101-an-intro-to-logging/

//
#logging with format:
logging.basicConfig(filename="sample.log", filemode="w", level=logging.INFO, format='%(asctime)s %(levelname)s %(message)s')
//
*Enumeration in Python
from enum import Enum
class Color(Enum):
    red = 1
    green = 2
    blue = 3

>>>print(Color.red.name)
red
>>>print(Color.red.value)
1

# supports iteration
for color in Color:
    print color.value
//
*group a list into inclusive sequential n-tuples
>>> lst = ['A', 'B', 'C', 'D', 'E', 'F', 'G']
>>> zip(lst, lst[1:])
[('A', 'B'), ('B', 'C'), ('C', 'D'), ('D', 'E'), ('E', 'F'), ('F', 'G')]
//
#iterating and printing all instances in a class
class A(object):
    def __init__(self):
        self.myinstatt1 = 'one'
        self.myinstatt2 = 'two'
    def mymethod(self):
        pass

a = A()
for attr, value in a.__dict__.iteritems(): # this is in python2, in
python use 3 dict.items()
    print attr, value
//
*checking if an element is on a list:
>>> a_list=['a','b','c','d']
>>> 'c' in a_list
False
//
*How to get list index and element simultaneously:
for k,i in enumerate(mylist):
    #do something with index k
    #do something with element i

#creating venn diagrams:
#2way
from matplotlib import pyplot as plt
from matplotlib_venn import venn2, venn2_circles
set1 = set(['A', 'B', 'C', 'D'])
set2 = set(['B', 'C', 'D', 'E'])

venn2([set1, set2], ('Set1', 'Set2'))

#3way
from matplotlib import pyplot as plt
from matplotlib_venn import venn3, venn3_circles
set1 = set(['A', 'B', 'C', 'D'])
set2 = set(['B', 'C', 'D', 'E'])
set3 = set(['C', 'D',' E', 'F', 'G'])

venn3([set1, set2, set3], ('Set1', 'Set2', 'Set3'))
//
#Venn with counts:

from collections import Counter
import matplotlib.pyplot as plt
from matplotlib_venn import venn2, venn3

%matplotlib inline

sets = Counter()
sets['01'] = 10
sets['11'] = 3
sets['10']  = 5
setLabels = ['set1', 'set2']

plt.figure()
ax = plt.gca()
v = venn2(subsets = sets, set_labels = setLabels, ax = ax)
plt.title('Venn Diagram')
plt.show()
//
#creating hist:
n, bins, patches = plt.hist(data, 50, normed=0, facecolor='green',
alpha=0.75,  range=[0, 990])

//
#adding y-label to a pyplot
plt.ylabel('some numbers')
//
#adding title to pyplot
plt.title('Histogram of IQ')
//
#adding a grid
plt.grid(True)
//
#importing an excel spreadsheet in Python:

import xlrd
#----------------------------------------------------------------------
def open_file(path):
    """
    Open and read an Excel file
    """
    book = xlrd.open_workbook(path)
    # print number of sheets
    print book.nsheets
    # print sheet names
    print book.sheet_names()
    # get the first worksheet
    first_sheet = book.sheet_by_index(0)
    # read a row
    print first_sheet.row_values(0)
    # read a cell
    cell = first_sheet.cell(0,0)
    print cell
    print cell.value
    # read a row slice
    print first_sheet.row_slice(rowx=0,
                                start_colx=0,
                                end_colx=2)
#----------------------------------------------------------------------
if __name__ == "__main__":
    path = "test.xls"
    open_file(path)

#using panda to load an excel file into a dataframe

# import modules
import pandas as pd
# Import the excel file and call it xls_file
xls_file = pd.ExcelFile('../data/example.xls')
xls_file
<pandas.io.excel.ExcelFile at 0x111912be0>
# View the excel file's sheet names
xls_file.sheet_names
['Sheet1']
# Load the xls file's Sheet1 as a dataframe
df = xls_file.parse('Sheet1')
df
/
#Load the xls file'e Sheet as a dataframe, skipping the first row:
df = xls_file.parse('Final QC Results',skiprows=1)

#Load the xls file'e Sheet as a dataframe, declaring a column as the index
df = xls.parse('Sheet1', index_col='Sample')

#Now declaring more than 1 column as the index:
df = xls.parse('Sheet1', index_col=[0,1])

* Now enforcing the type of some of the columns:
df = xls.parse('Sheet1', index_col=[0,1],converters={'A': str})
//
>>> writer = pd.ExcelWriter('output.xlsx')
>>> df1.to_excel(writer,'Sheet1')
>>> df2.to_excel(writer,'Sheet2')
>>> writer.save()
//
#  In python 2.7, the integer division truncates the result. For example:
>>> 3 / 2
1
# Use this instead:
>>> from __future__ import division
>>> 53740/3
17913.333333333332
//
#checking if a str is a float or int:
import sys

def numeric_type(x):
    type=""
    try:
        a = float(x)
        if a.is_integer()==True:
           type="int"
        else:
            type="float"
    except ValueError:
        type="str"
    return type

s=sys.argv[1]

print numeric_type(s)

import sys

def numeric_type(x):
    type=""
    try:
        a = float(x)
        if a.is_integer()==True:
           type="int"
        else:
            type="float"
        return type
    except ValueError:
        return False

s=sys.argv[1]

print numeric_type(s)
//
#python one-liner:

python -c "for r in range(10): print r"
//
#what is an __init__.py file:
Read documentation at:
https://pythontips.com/2013/07/28/what-is-__init__-py/
//
*DUMMIFY (or Convert A Categorical Variable Into Dummy Variables):
# import modules
import pandas as pd
# Create a dataframe
raw_data = {'first_name': ['Jason', 'Molly', 'Tina', 'Jake', 'Amy'], 
        'last_name': ['Miller', 'Jacobson', 'Ali', 'Milner', 'Cooze'], 
        'sex': ['male', 'female', 'male', 'female', 'female']}
df = pd.DataFrame(raw_data, columns = ['first_name', 'last_name', 'sex'])
df

	first_name	last_name	sex
0	Jason	Miller	male
1	Molly	Jacobson	female
2	Tina	Ali	male
3	Jake	Milner	female
4	Amy	Cooze	female

# Create a set of dummy variables from the sex variable
df_sex = pd.get_dummies(df['sex'])

# Join the dummy variables to the main dataframe
df_new = pd.concat([df, df_sex], axis=1)
df_new


first_name	last_name	sex	female	male
0	Jason	Miller	male	0	1
1	Molly	Jacobson	female	1	0
2	Tina	Ali	male	0	1
3	Jake	Milner	female	1	0
4	Amy	Cooze	female	1	0
//
#serializing a dataframe (store)
df.to_pickle(file_name)  # where to save it, usually as a .pkl

#Then you can load it back using:
df = pd.read_pickle(file_name)
//
#ipython. Embedding images:
from IPython.display import Image
Image("/Users/ernesto/Desktop/20170301124551634.png")
//
*Compute the skewness of a dataset
scipy.stats.skew(a, axis=0, bias=True)[source]¶
//
#generate a random string in python
>>> import string
>>> import random
>>> def random_generator(size=6, chars=string.ascii_uppercase + string.digits):
...    return ''.join(random.choice(chars) for x in range(size))
...
>>> random_generator()
'G5G74W'
>>> random_generator(3, "6793YUIO")
'Y3U'1
//
#Converting a string representation of a list into an actual list object
>>> fruits = "['apple', 'orange', 'banana']"
>>> import ast
>>> fruits = ast.literal_eval(fruits)
>>> fruits
['apple', 'orange', 'banana']
>>> fruits[1]
'orange'
//
#How to use the __init__.py 
Files named __init__.py are used to mark directories on disk as Python package directories. If you have the files

mydir/spam/__init__.py
mydir/spam/module.py

and mydir is on your path, you can import the code in module.py as

import spam.module

or

from spam import module

#good explanation on what is a @classmethod 
https://stackoverflow.com/questions/12179271/meaning-of-classmethod-and-staticmethod-for-beginner
#
#compare 2 lists and return matches
>>> a = [1, 2, 3, 4, 5]
>>> b = [9, 8, 7, 6, 5]
>>> set(a) & set(b)
//
#check if 2 lists are equal (order does not matter):
>>> a = [1, 2, 3, 4, 5]
>>> b = [9, 8, 7, 6, 5]
>>> set(a)==set(b)    
//
#creating a temporary file and write something to it and read it from it
#the file is destroyed when temp.close() is called

import os
import tempfile

temp = tempfile.TemporaryFile()
try:
    temp.write('Some data')
    temp.seek(0)

    print temp.read()
finally:
    temp.close()

#creating a temporary file with a name (path) associated to it:

import os
import tempfile

temp = tempfile.NamedTemporaryFile()
try:
    print 'temp:', temp
    print 'temp.name:', temp.name
finally:
    # Automatically cleans up the file
    temp.close()
print 'Exists after close:', os.path.exists(temp.name)
//
#parse file with entries (each entry on a newline) and create a list:
crimefile = open('chros.txt', 'r')

lines = crimefile.read().splitlines()
//
temp = tempfile.NamedTemporaryFile(dir='testdir/',delete=False,prefix='caca')
//
* Running pylint:
Run pylint and generate a report:
pylint --reports=y VcfFilter.py
//
#pytest
######################################
/
#creating a simple test with a fixture

@pytest.fixture
def some_data():
    return 42

def test_some_data(some_data):
    assert some_data == 42

#some_data() can be used by different test functions 

/
#creating tmp files
import os
def test_create_file(tmpdir):
    p = tmpdir.mkdir("sub").join("hello.txt")
    p.write("content")
    assert p.read() == "content"
    assert len(tmpdir.listdir()) == 1
    assert 0
/
#in this fixture we execute code within the fixture before the test, 
then we pass 42 to the test with yield and finally we execute the code
after the yield that is executed at the end:

import pytest
import warnings

@pytest.fixture
def some_data():
    warnings.warn("before the test")
    yield 42
    warnings.warn("executed after the test")


def test_some_data(some_data):
    warnings.warn("executed in the test")
    assert some_data == 42
/
pytest -s #will invoke pytest and write the output of the print commands to the terminal
//
#pytest check that raises and Exception:
def test_passes():
    with pytest.raises(Exception) as e_info:
        x = 1 / 0
#########################################
#dropping trailing 0s
a="1.00000"
(str(a)[-2:] == '.0' and str(a)[:-2] or str(a))

1
//
# asserting for equality of a returned list in pytest:
returned_list=['a','b','c']

assert all([a == b for a, b in zip(returned_list, ['a','b','c'])])
//
# how to check if a file is a directory or regular file in python?
os.path.isfile("bob.txt") # Does bob.txt exist?  Is it a file, or a directory?
os.path.isdir("bob")
//
* Python: access class property from string

x = getattr(self, source)
//
# parse a string representing a list into a real list
>>> import ast
>>> mylist = ast.literal_eval("['foo', ['cat', ['ant', 'bee'], 'dog'], 'bar', 'baz']")
>>> mylist
['foo', ['cat', ['ant', 'bee'], 'dog'], 'bar', 'baz']
//
#Create a List that contain each Line of a File

List = open("filename.txt").readlines()
//
# creating a dir if it does not exist:
if not os.path.exists(directory):
    os.makedirs(directory)
//
# convert a list into a string:
list1 = ['1', '2', '3']
str1 = ''.join(list1)
//
#good tutorial on Python decorators:
https://realpython.com/primer-on-python-decorators/
//
# requests module
# Get a website from the internet:
#
#Create a program called anexample.py:
def simple_get(url):
    """
    Attempts to get the content at `url` by making an HTTP GET request.
    If the content-type of response is some kind of HTML/XML, return the
    text content, otherwise return None
    """
    try:
        with closing(get(url, stream=True)) as resp:
            if is_good_response(resp):
                return resp.content
            else:
                return None

    except RequestException as e:
        log_error('Error during requests to {0} : {1}'.format(url, str(e)))
        return None


def is_good_response(resp):
    """
    Returns true if the response seems to be HTML, false otherwise
    """
    content_type = resp.headers['Content-Type'].lower()
    return (resp.status_code == 200 
            and content_type is not None 
            and content_type.find('html') > -1)


def log_error(e):
    """
    It is always a good idea to log errors. 
    This function just prints them, but you can
    make it do anything.
    """
    print(e)

#Then:
>>> from anexample import simple_get
>>> raw_html = simple_get('https://realpython.com/blog/')
>>> len(raw_html)
33878
//
#adding timestamp to filename:
import time
timestr = time.strftime("%Y%m%d-%H%M%S")
print timestr

#Packaging:

#To create a release, your source code needs to be packaged into a single archive file. This can be done with the sdist command:
python setup.py sdist

This command will create the *.tar.gz file inside ./dist/

#Then we can install it by doing:
pip install ./dist/package.tar.gz
//
#getters and setters (the pythonic way):
# Excellent post at: https://www.programiz.com/python-programming/property

class Celsius:
    def __init__(self, temperature = 0):
        self._temperature = temperature

    def to_fahrenheit(self):
        return (self.temperature * 1.8) + 32

    @property
    def temperature(self):
        print("Getting value")
        return self._temperature

    @temperature.setter
    def temperature(self, value):
        if value < -273:
            raise ValueError("Temperature below -273 is not possible")
        print("Setting value")
        self._temperature = value
	
//
#Sphinx . Generating documentation:
/
#Generate automatically doc for your source dir
sphinx-apidoc -o /homes/ernesto/lib/igsr_analysis/docs/ /homes/ernesto/lib/igsr_analysis/
# In this case, -o sets where to put the generated doc, and the second parameter sets the path to the source code
//
#sorting a list of tuples by first element then by the second
unsorted = [('a', 4, 2), ('a', 4, 3), ('a', 7, 2), ('a', 7, 3), ('b', 4, 2), ('b', 4, 3), ('b', 7, 2), ('b', 7, 3)]

print(sorted(unsorted, key=lambda element: (element[1], element[2])))
//
# Getting information on the different numeric Python data types

import numpy as np

int_types = ["uint8", "int8", "int16"]
for it in int_types:
    print(np.iinfo(it))

float_types = ["float16", "float32", "float64"]
for ft in float_types:
    print(np.finfo(ft))
//
# Memory profiling
#Install required module:
pip install  -U memory_profiler

#Create a test function and decorate it with @profile:
@profile
def my_func():
    a = [1] * (10 ** 6)
    b = [2] * (2 * 10 ** 7)
    del b
    return a

if __name__ == '__main__':
    my_func()
    
#Finally run the test script in the following way:
 python -m memory_profiler test.py
 
//
# initializing several lists at the same time:
 alist, blist, clist, dlist, elist = ([] for i in range(5))
//
# Generating tables in python
from prettytable import PrettyTable

x = PrettyTable()

# we set the header
x.field_names = ["City name", "Area", "Population", "Annual Rainfall"]
 
# we add values 
x.add_row(["Adelaide", 1295, 1158259, 600.5])
x.add_row(["Brisbane", 5905, 1857594, 1146.4])
 
print(x)

+-----------+------+------------+-----------------+
| City name | Area | Population | Annual Rainfall |
+-----------+------+------------+-----------------+
|  Adelaide | 1295 |  1158259   |      600.5      |
|  Brisbane | 5905 |  1857594   |      1146.4     |
|   Darwin  | 112  |   120900   |      1714.7     |
|   Hobart  | 1357 |   205556   |      619.5      |
|   Sydney  | 2058 |  4336374   |      1214.8     |
| Melbourne | 1566 |  3806092   |      646.9      |
|   Perth   | 5386 |  1554769   |      869.4      |
+-----------+------+------------+-----------------+
//
#checking if an int is within 2 numbers:
if 10000 <= number <= 30000:
//
* check if something is list
x = {'a', 'b', 'c', 'd'}

if type(x) is list:
	print("h")
//
# How to check if an object has an attribute in Python:
hasattr(self, 'start')
True
//
#append elements to beginning of list :
>>> a = ['a','b']
>>> k = ['nice', '-n', '10']
>>> a[0:0] = k
>>> a
['nice', '-n', '10', 'a', 'b']
//
#remove several elements from a list using its index
item_list = ['item', 5, 'foo', 3.14, True]
item_list = [e for e in item_list if e not in ('item', 5)]
//
# generating ranges in python
#Create a sequence of numbers from 3 to 5, and print each item in the sequence:
x = range(3, 6)
for n in x:
  print(n)
#Create a sequence of numbers from 3 to 19, but increment by 2 instead of 1:
x = range(3, 20, 2)
for n in x:
  print(n)
  * Article on how to manage configuration files in python:
  https://hackernoon.com/4-ways-to-manage-the-configuration-in-python-4623049e841b
 //
 # remove several elements from a list
indices = [0, 2]
somelist = [i for j, i in enumerate(somelist) if j not in indices]
 //
 # Iterating over every two elements in a list
 
 l = [1,2,3,4,5,6]

def pairwise(iterable):
    "s -> (s0, s1), (s2, s3), (s4, s5), ..."
    a = iter(iterable)
    return zip(a, a)

for x, y in pairwise(l):
   print("{0} + {1} = {2}".format(x, y, x + y))
  
 //
 # Making a Python script executable:
 1) Add this line as the first line in the script: #!/usr/bin/env python3.
2) At the unix command prompt, type the following to make myscript.py executable: $ chmod +x myscript.py.
 //
 * Previous and next values inside a loop
 Example extracted from:
https://stackoverflow.com/questions/1011938/python-previous-and-next-values-inside-a-loop

 from itertools import tee, islice, chain, izip

def previous_and_next(some_iterable):
    prevs, items, nexts = tee(some_iterable, 3)
    prevs = chain([None], prevs)
    nexts = chain(islice(nexts, 1, None), [None])
    return izip(prevs, items, nexts)
 
 mylist = ['banana', 'orange', 'apple', 'kiwi', 'tomato']

for previous, item, nxt in previous_and_next(mylist):
    print "Item is now", item, "next is", nxt, "previous is", previous

The results:
Item is now banana next is orange previous is None
Item is now orange next is apple previous is banana
Item is now apple next is kiwi previous is orange
Item is now kiwi next is tomato previous is apple
Item is now tomato next is None previous is kiwi
//
# Excellent articule on decorators:
https://realpython.com/primer-on-python-decorators/#simple-decorators
//
#knowing PYTHONPATH from python script
import os
try:
    user_paths = os.environ['PYTHONPATH'].split(os.pathsep)
    print(user_paths)
except KeyError:
    user_paths = []
//
# Excellent artickle on how to submit a Python project to PyPi
https://dzone.com/articles/executable-package-pip-install
//
# How to use glob() to find files recursively?
from pathlib import Path

for filename in Path('src').rglob('*.c'):
    print(filename)
//
# Convert Python2 code to Python3
# Where test.py contains the code to modify, with -w we will
# print out on the same file

2to3 -w test.py
//
# Excellent article on using the main entry point in Python
https://realpython.com/python-main-function/
//
# Python shebang or hash bang:
#!/usr/bin/python: writing the absolute path
#!/usr/bin/env python: using the operating system env command, which locates 
and executes Python by searching the PATH environment variable
//
main entry point with args parsing:
import argparse

def main():
    parser = argparse.ArgumentParser()
    parser.add_argument('file_in', help='input file')
    parser.add_argument('file_out', help='output file')
    args = parser.parse_args()
    execute_code(args.file_in, args.file_out)

if __name__ == '__main__':
    main()
//
# Splitting a string by one or more whitespaces
import re

str = '63 41    92  81            69  70'

#split string by single space
chunks = re.split(' +', str)

print(chunks)

//
# Testing if a binary exists
def is_tool(name):
    """Check whether `name` is on PATH and marked as executable."""

    # from whichcraft import which
    from shutil import which

    return which(name) is not None

//
% modulo operator
a = 9
b = 3
answer = a % b

print(answer)

which_equivalent.py

# Python program to explain shutil.which() method 
# check if python is in PATH
      
# importing os module 
import os 
  
# importing shutil module 
import shutil 
  
# cmd 
cmd = 'python'
  
# Using shutil.which() method
locate = shutil.which(cmd)
  
# Print result
print(locate) # outputs: /usr/bin/python