Python

1 - ############ built-in zip function for i, j in zip(list1, list2)

2 - ############ built-in enumerate function for i,j in enumerate(lista) i = indice j = element

3 - ############ accessing a global variable a = 10 def foo(): global a a = 10

4 - ########### range performance

Python 2.7

for i in range(100):

Bad Idea, range will be evaluate each loop iteration

a = range(100) for i in a:

Good Idea

or

for i in xrange(100)

xrange is a Yield

Python 3

range == xrange in Python 2.7

5 - ########## avoiding Dictionaries KeyError dict.get(key, default) instead of dict[key]

6 - ########## for else for i in xrange(10): pass else: # Else means, no brak pass

7 - ########## try excepet else finally

Python 2.7

try: pass except Exception, e: raise else: # Else means no exception pass finally: # It will always execute pass

Python 3

try: 1/0 except (Exception, ZeroDivisionError) as e: print(e) else: print('No exception') finally: print('Finally')

8 - ########## List comprehension m = [e for i in range(0, 10) for e in range(5) if ((e%2==0))] m = [(i,e) for i in range(0, 10) for e in range(5) if ((e%2==0))]

9 - ########## String parameters Python print ("%d" % 10) print ("%d %s %.2f" % (10, 'Gp', 1.2)) print ("{name} {age}".format(name='Gp', age=28)) print ("%s %d".format('Gp', 28)) # Doesn't work lista = ['Gp', 28] print ("{0} {1}".format(*lista)) dic = {'name': 'Gp', 'age': 28} print ("{name} {age}".format(**dic)) nome = 'Gp' idade = 28 print('Ola, meu nome e %(nome)s, eu tenho %(idade)d anos.' % vars())

10 - ######### Args and kwargs Python def f(args): # You use args when you don't know how many arguments might be passed print(type(args)) # list for i in args: print i

f([1,2,2]) t = (2,3,4,4) f(t) l = [3,3,3] f(l)

if you put * in the assinment parameters you should call the function puttin

def f2(**args): # **kwargs allows you to handle named arguments that you have not defined in advance print(type(args)) # print dict for name, value in args.iteritems(): print name, value

f2(key1=10, key2=20) f2({'g': 99, 'h':100}) # It doesn't work if you dont put **

11 - ######### Operations Python 2.7

10/3 = 3 10//3. = 3.0 # Doble slashes forces round down

Python 3 10/3 = 3.3333333 10//3. = 3.0 # Doble slashes forces round down

12 - ######### Tuples vs Lists Tuple, Imutable, less memory Lists, Mutable, More memory

13 - ########## Named parameters def f(a,b,c=10): print(a,b,c)

f(10,20,20) f(10,20) f(a=10, b=10) f(a=10, c=10) # it doesn't work

14 - ########## Yeild def primeiros(n): i = 0 while i < n: yield i i += 1 else: yield 'Fim'

for i in primeiros(10): print i

15 - ########## OO constructor class Doc(object): def init: self.name = 'rex'

16 - ########## OO Inheritance class dog(object): def init(self): print 'Object instaciate'

    def latir(self, ofthen):
            print 'Au! ' * ofthen
class SaoBernardo(dog): def latir(self, ofthen = 1): print 'Woof! ' * ofthen

c = dog() c.latir(1)

d = SaoBernardo() d.latir(10)

Object instaciate Au! Object instaciate Woof! Woof! Woof! Woof! Woof! Woof! Woof! Woof! Woof! Woof!

17 - ########## OO Super class SaoBernardo(dog): def latir(self, ofthen = 1): super(SaoBernardo, self).latir(ofthen=2)

18 - ########## OO accessing private atributes myObj._ClassName__myPrivateMethod()

19 - ########## property/getter, setter, deleter class C(object): def init(self): self._x = None

@property
def getX(self):
    print 'Getter'
    return self._x

@getX.setter
def setX(self, value):
    print 'Setter'
    self._x = value

@getX.deleter
def delX(self):
    print 'Delete'
    del self._x
20 - ########## Iterators

21 - ########## Generators

22 - ########## Lambga m = [lambda x , i=i: (i * x) for i in range(3)] x pararameter i=i fixing i in each iteration (i*x) return

23 - ########## Map n = [2,4,6,8] print map(lambda x: x**2, n) [4, 16, 36, 64]

Python 3 l = ['1', '2'] l = list(map(int, l))

24 - ########## Reduce n = [2,3,4,5,6] print reduce(lambda x, y : x + y, n)

20

25 - ########## Filter

Filter just return True elements

n = [2,3,4,5,6,7,8,9,10] print filter(lambda x : x if x % 2 == 0 else None, n)

26 - ########## Shallow copy and Deep Copy

27 - ########## input input().strip() Remove spaces from the begining and ending of string inputed

28 - ######## Threads #!/usr/bin/python

import thread import time

Define a function for the thread

def print_time( threadName, delay):

count = 0

while count < 5:

  time.sleep(delay)

  count += 1

  print "%s: %s" % ( threadName, time.ctime(time.time()) )
Create two threads as follows

try:

thread.start_new_thread( print_time, ("Thread-1", 2, ) )

thread.start_new_thread( print_time, ("Thread-2", 4, ) )

except:

print "Error: unable to start thread"

while 1:

pass

29 - #######
import calendar
from dateutil import relativedelta

last_month = datetime.now() - relativedelta.relativedelta(months=1)
last_day_last_month = calendar.monthrange(year=last_month.year, month=last_month.month)