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My Python Cheatsheet
Python Cheatsheet
=================
################################ Input & Output ###############################
name = input('please enter your name: ')
print('hello,', name)
ageStr = input('please enter your age: ')
age = int(ageStr)
#################################### String ####################################
"I'm OK"
'I\'m \"OK\"!'
r'\\\t\\'
'''line1
line2
line3'''
################################ Python's Null ################################
None
################################### Division ###################################
10 / 3
10 // 3
10 % 3
############################## Unicode <--> char ##############################
ord('A')
chr(66)
'\u4e2d\u6587'
#################################### Bytes ####################################
b'ABC'
############################### Encode & Decode ###############################
'中文'.encode('utf-8')
b'\xe4\xb8\xad\xe6\x96\x87'.decode('utf-8')
'ABC'.encode('ascii')
b'ABC'.decode('ascii')
################################ String format ################################
'Hi, %s, you have $%d.' % ('Michael', 1000000)
'%.2f' % 3.1415926
'Age: %s. Gender: %s' % (25, True) # bool->true
%d int
%f float
%s str
%x hex int
a = 'abc'
b = a.replace('a', 'A')
b # = 'Abc'
a # = 'abc'
##################################### List #####################################
classmates = ['Michael', 'Bob', 'Tracy']
len(classmates)
classmates[-1] = 'Sarah'
classmates.append('Adam')
classmates.insert(1, 'Jack')
classmates.pop()
L0 = []
L1 = ['Apple', 123, True]
L2 = ['python', 'java', ['asp', 'php'], 'scheme']
len(L2) # = 4;
################################ Slice of list ################################
L = ['Michael', 'Sarah', 'Tracy', 'Bob', 'Jack']
L[0:3] # = ['Michael', 'Sarah', 'Tracy']
L[:3] # same
L[:-2] # same
L = list(range(100))
L[:10:2] # = [0, 2, 4, 6, 8]
L[::5] # [0, 5, 10, 15, 20, 25, 30 ... 90, 95]
L[:] # [0, 1, 2, 3, ..., 99]
#################################### Tuple ####################################
classmates = ('Michael', 'Bob', 'Tracy')
classmates[-1]
t = ()
t = (1,) # attention comma!
t = (1, 2)
################################# Other slice #################################
(0, 1, 2, 3, 4, 5)[:3] # = (0, 1, 2)
'ABCDEFG'[:3]
################################ 'if' statement ################################
age = 20
if age >= 6:
print('teenager')
elif age >= 18:
print('adult')
else:
print('kid')
if x:
print('True')
# x -> True when x is:
# non-zero int, non-empty str, non-empty list/tuple
############################### 'for' statement ###############################
names = ['Michael', 'Bob', 'Tracy']
for name in names:
print(name)
list(range(5)) # = [0, 1, 2, 3, 4]
sum = 0
for x in range(101):
sum = sum + x
############################## 'while' statement ##############################
sum = 0
x = 100
while x > 0:
sum = sum + x
x = x - 1
################################ Key-value dict ################################
d = {'Michael': 95, 'Bob': 75, 'Tracy': 85}
d['Michael'] # Get (= 95)
d['Adam'] = 67 # Insert
d['Adam'] = 90 # Replace
'Thomas' in d # False
d.get('Thomas', -1) # -1
d.pop('Bob') # Delete
##################################### Set #####################################
s = set([1, 2, 3])
set([1, 1, 2, 2, 3, 3]) # {1, 2, 3}
s.add(4) # no effect if duplicated
s.remove(4)
s1 & s2 # intersection
s1 | s2 # union
##################################### Math #####################################
abs(-100)
max(3, 2, -3, -5)
############################### Type convertion ###############################
int('123')
int(12.34)
float('12.34')
str(1.23)
str(100)
bool(1) # True
bool('') # False
############################### 'pass' statement ###############################
def nop():
pass
if age >= 18:
pass
############################ 'isinstance' statement ############################
if not isinstance(x, (int, float)):
raise TypeError('bad operand type')
############################# return multi values #############################
def move(x, y, step, angle=0):
nx = x + step * math.cos(angle)
ny = y - step * math.sin(angle)
return nx, ny
x, y = move(100, 100, 60, math.pi / 6)
ret = move(...) # -> tuple
##################### Named arguments & default arguments #####################
def enroll(name, gender, age=6, city='Beijing'):
print('name:', name)
print('gender:', gender)
print('age:', age)
print('city:', city)
enroll('Sarah', 'F')
enroll('Bob', 'M', 7)
enroll('Adam', 'M', city='Tianjin')
def add_end(L=[]): # L is created every time
L.append('END')
return L
add_end() # ['END']
add_end() # ['END', 'END']
add_end() # ['END', 'END', 'END']
# corrected:
def add_end(L=None):
if L is None:
L = []
L.append('END')
return L
################################### '*args' ###################################
def calc(*numbers): # arg list -> tuple
sum = 0
for n in numbers:
sum = sum + n * n
return sum
calc(1, 2)
calc(1, 2, 3)
calc()
calc(*nums) # list/tuple -> arg list
################################## '**kwargs' ##################################
def person(name, age, **kw): # arg list -> dict
print('name:', name, 'age:', age, 'other:', kw)
person('Michael', 30) # kw = {}
person('Bob', 35, city='Beijing')
# kw = {'city': 'Beijing'}
person('Adam', 45, gender='M', job='Engineer')
# kw = {'gender': 'M', 'job': 'Engineer'}
extra = {'city': 'Beijing', 'job': 'Engineer'}
person('Jack', 24, **extra) # dict -> arg list
################################# Named params #################################
def person(name, age, *, city='Beijing', job):
print(name, age, city, job)
person('Jack', 24, city='Beijing', job='Engineer')
person('Jack', 24, 'Beijing', 'Engineer') # error
############################### Iterator on dict ###############################
d = {'a': 1, 'b': 2, 'c': 3}
for key in d:
print(key) # a b c
for value in d.values():
print(value) # 1 2 3
for k, v in d.items():
print(k, v)
################################### Iterable ###################################
from collections import Iterable
isinstance('abc', Iterable) # True
isinstance(123, Iterable) # False
################################ List Generator ################################
[x * x for x in range(1, 11)]
[x * x for x in range(1, 11) if x % 2 == 0]
[m + n for m in 'ABC' for n in 'XYZ']
[k + '=' + v for k, v in d.items()]
L = ['Hello', 'World', 'IBM', 'Apple']
[s.lower() for s in L]
################################## Generator ##################################
(x * x for x in range(10))
next(g) # 0
next(g) # 1
next(g) # 4 ...
G = (x * x for x in range(10))
for n in G:
print(n)
def fib(max):
n, a, b = 0, 0, 1
while n < max:
yield b
a, b = b, a + b
n = n + 1
return 'done'
object = fib(10) # type = genetator object
def triangles():
result = [1]
while True:
yield result
a, b = [0] + result, result + [0]
result = [a[i] + b[i] for i in range(len(a))]
######################### Iterable / Iterator / iter() #########################
isinstance('abc', Iterable) # True
isinstance('abc', Iterator) # False
isinstance(iter('abc'), Iterator) # True
############################ Higher-order functions ############################
def add(x, y, f):
return f(x) + f(y)
add(-5, 6, abs) # = abs(-5) + abs(6) = 11
##################################### map #####################################
it = map(abs, [-1, -2, -3]) # iterator
list(it) # [1, 2, 3]
#################################### reduce ####################################
# reduce(f, [x1, x2, x3, x4]) = f(f(f(x1, x2), x3), x4)
from functools import reduce
def add(x, y):
return x + y
reduce(add, [1, 3, 5, 7, 9]) # 25
from functools import reduce
def char2num(s):
return {'0': 0, '1': 1, '2': 2, '3': 3, '4': 4, '5': 5, '6': 6, '7': 7, '8': 8, '9': 9}[s]
def str2int(s):
return reduce(lambda x, y: x * 10 + y, map(char2num, s))
#################################### filter ####################################
def is_odd(n):
return n % 2 == 1
list(filter(is_odd, [1, 2, 4, 5, 6, 9, 10, 15])) # = [1, 5, 9, 15]
# or: for x in filter(..) ....
################################### Sorting ###################################
sorted(['bob', 'about', 'Zoo', 'Credit'])
# ['Credit', 'Zoo', 'about', 'bob']
sorted(['bob', 'about', 'Zoo', 'Credit'], key=str.lower)
# ['about', 'bob', 'Credit', 'Zoo']
sorted(['bob', 'about', 'Zoo', 'Credit'], key=str.lower, reverse=True)
# ['Zoo', 'Credit', 'bob', 'about']
############################## Return a function ##############################
def lazy_sum(*args):
def sum():
ax = 0
for n in args:
ax = ax + n
return ax
return sum
f = lazy_sum(1, 3, 5, 7, 9)
f # function
f() # 25
################################### Closure ###################################
def count():
def f(j): # Bind i->j
def g():
return j*j
return g
fs = []
for i in range(1, 4):
fs.append(f(i))
return fs
f1, f2, f3 = count()
################################## Decorator ##################################
import functools
def log(text):
def decorator(func):
@functools.wraps(func) # 把func的name等属性复制给wrapper
def wrapper(*args, **kw):
print('%s %s():' % (text, func.__name__))
return func(*args, **kw)
return wrapper
return decorator
@log("call")
def now():
print('2015-3-25')
now()
# call now():
# 2015-3-25
############################## A Standard Module ##############################
#!/usr/bin/env python3
# -*- coding: utf-8 -*-
' a test module '
__author__ = 'Michael Liao'
import sys
def test():
args = sys.argv
if len(args)==1:
print('Hello, world!')
elif len(args)==2:
print('Hello, %s!' % args[1])
else:
print('Too many arguments!')
if __name__=='__main__':
test()
#################################### Class ####################################
class Student:
def __init__(self, name, score):
self.__name = name
self.__score = score
def print_score(self):
print('%s: %s' % (self.__name, self.__score))
################################### Inherit ###################################
class Animal:
def run(self):
print('Animal is running...')
class Dog(Animal):
pass
class Tortoise(Animal):
def run(self):
print('Tortoise is running slowly...')
class Runnable:
def run(self):
print('Running...')
class Husky(Mammal, Runnable): # multi
pass
########################### Some built-in functions ###########################
isinstance(h, Husky)
isinstance(h, (int, float))
dir(object)
getattr(obj, 'attr')
setattr(obj, 'attr', 123)
hasattr(obj, 'attr')
class Student:
common_attr = 'hello'
def common_func():
pass
#################################### Slots ####################################
class Student(object):
__slots__ = ('name', 'age')
################################### Property ###################################
class Student:
@property
def score(self):
return self._score
@score.setter
def score(self, value):
if not isinstance(value, int):
raise ValueError('score must be an integer!')
if value < 0 or value > 100:
raise ValueError('score must between 0 ~ 100!')
self._score = value
s = Student()
s.score = 60 # OK, -> s.set_score(60)
s.score # OK -> s.get_score() -> 60
######################### Built-in functions of object #########################
__str__(self)
__repr__(self) # __repr__ = __str__
__iter__(self) # return an iterator object
__getitem__(self, n_or_slice) # [n] [n:m]
__getattr__(self, attr_name)
__call__(self)
################################## Enumerate ##################################
enumerate(['A', 'B', 'C']) # {0:'A', 1:'B', 2:'C'}
for i, value in enumerate(['A', 'B', 'C']):
print(i, value)
from enum import Enum
Month = Enum('Month', ('Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec'))
Month.Jan # == 1. Enum begins from 1
Month['Jan']
Month(1)
for name, member in Month.__members__.items():
print(name, '=>', member, ',', member.value)
############################ Another usage of enum ############################
from enum import Enum, unique
@unique # make sure no duplicated values
class Weekday(Enum):
Sun = 0 # set Sun = 0
Mon = 1
Tue = 2
Wed = 3
Thu = 4
Fri = 5
Sat = 6
######################## 'try' statement and exception ########################
try:
print('try...')
r = 10 / 0
print('result:', r)
except ZeroDivisionError as e:
print('except:', e)
else:
pass
finally:
print('finally...')
print('END')
class FooError(ValueError):
pass
raise FooError('invalid value: %s' % s)
################################ logging module ################################
import logging
logging.exception(e)
logging.info('info') # debug, info, warning, error
logging.basicConfig(level=logging.INFO)
############################## 'assert' statement ##############################
assert n != 0, 'n is zero!'
# python -O to shut down asserts
################################## Unit test ##################################
import unittest
from mydict import Dict
class TestDict(unittest.TestCase):
def test_init(self):
d = Dict(a=1, b='test')
self.assertEqual(d.a, 1)
self.assertEqual(d.b, 'test')
self.assertTrue(isinstance(d, dict))
def test_keyerror(self):
d = Dict()
with self.assertRaises(KeyError):
value = d['empty']
def other_func(self): # not run
pass
def setUp(self):
print('setUp...')
def tearDown(self):
print('tearDown...')
if __name__ == '__main__':
unittest.main()
# or python3 -m unittest mydict_test
################################### Doctest ###################################
# `...` for some output
class Dict(dict):
'''
Simple dict but also support access as x.y style.
>>> d1 = Dict()
>>> d1['x'] = 100
>>> d1.x
100
>>> d1.y = 200
>>> d1['y']
200
>>> d2 = Dict(a=1, b=2, c='3')
>>> d2.c
'3'
>>> d2['empty']
Traceback (most recent call last):
...
KeyError: 'empty'
>>> d2.empty
Traceback (most recent call last):
...
AttributeError: 'Dict' object has no attribute 'empty'
'''
############################### File Operations ###############################
f = open('/Users/michael/notfound.txt', 'r')
f.read() # read all -> str
f.readline()
f.read(size_in_bytes)
f.readlines() # -> list
f.close()
with open('/path/to/file', 'r') as f:
for line in f.readlines():
print(line.strip()) # delelte '\n'
# close when leaving 'with' block
f = open('/Users/michael/test.jpg', 'rb')
f.read() # -> bytes
f = open('/Users/michael/gbk.txt', 'r', encoding='gbk')
f.read() # -> str
f = open('/Users/michael/gbk.txt', 'r', encoding='gbk', errors='ignore')
f = open('/Users/michael/test.txt', 'w')
f.write('Hello, world!')
f.close()
with open('/Users/michael/test.txt', 'w') as f:
f.write('Hello, world!')
################################ String Buffer ################################
from io import StringIO
f.write('hello')
f.write('world!')
print(f.getvalue())
from io import StringIO
f = StringIO('Hello!\nHi!\nGoodbye!')
s = f.readline()
################################# Bytes Buffer #################################
from io import BytesIO
f = BytesIO()
f.write('中文'.encode('utf-8'))
print(f.getvalue())
################################# 'os' module #################################
import os
os.name # 'nt' for windows, 'posix' for linux/unix
os.environ
os.environ.get('PATH')
os.path.abspath('.')
os.path.join('/Users/michael', 'testdir')
os.mkdir('/Users/michael/testdir')
os.rmdir('/Users/michael/testdir')
os.path.split('/Users/michael/testdir/file.txt')
# ('/Users/michael/testdir', 'file.txt')
os.path.splitext('/path/to/file.txt')
# ('/path/to/file', '.txt')
os.rename('test.txt', 'test.py')
os.remove('test.py')
os.listdir('.')
[x for x in os.listdir('.') if os.path.isfile(x) and os.path.splitext(x)[1]=='.py']
############################### 'pickle' module ###############################
import pickle
d = dict(name='Bob', age=20, score=88)
pickle.dumps(d) # -> bytes
with open('dump.txt', 'wb') as f:
pickle.dump(d, f)
with open('dump.txt', 'rb') as f:
d = pickle.load(f)
################################ 'json' module ################################
import json
d = dict(name='Bob', age=20, score=88)
json.dumps(d) # -> str
json_str = '{"age": 20, "score": 88, "name": "Bob"}'
json.loads(json_str) # -> dict
json.load(file)
import json
class Student(object):
def __init__(self, name, age, score):
self.name = name
self.age = age
self.score = score
def student2dict(std):
return {
'name': std.name,
'age': std.age,
'score': std.score
}
print(json.dumps(s, default=student2dict))
print(json.dumps(s, default=lambda obj: obj.__dict__))
def dict2student(d):
return Student(d['name'], d['age'], d['score'])
json_str = '{"age": 20, "score": 88, "name": "Bob"}'
json.loads(json_str, object_hook=dict2student))
############################## Regular expression ##############################
import re
re.match(r'^\d{3}\-\d{3,8}$', '010-12345') # Match object or None
re.split(r'\s+', 'a b c') # ['a', 'b', 'c']
m = re.match(r'^(\d{3})-(\d{3,8})$', '010-12345')
m.group(0) # '010-12345'
m.group(1) # '010'
m.group(2) # '12345'
m.groups() # ('010', '12345')
re_telephone = re.compile(r'^(\d{3})-(\d{3,8})$')
re_telephone.match('010-12345')
################################# Data & Time #################################
from datetime import datetime
now = datetime.now()
print(now) # 2015-05-18 16:28:07.198690
dt = datetime(2015, 4, 19, 12, 20)
print(dt) # 2015-04-19 12:20:00
dt.timestamp() # 1429417200.0
dt = datetime.fromtimestamp(1429417200.0)
print(dt) # 2015-04-19 12:20:00
cday = datetime.strptime('2015-6-1 18:19:59', '%Y-%m-%d %H:%M:%S')
cday_str = cday.strftime('%a, %b %d %H:%M')
from datetime import datetime, timedelta
now = datetime.now()
now + timedelta(days=2, hours=12)
from datetime import datetime, timedelta, timezone
datetime.utcnow()
bj_dt = utc_dt.astimezone(timezone(timedelta(hours=8)))
################################# Named tuple #################################
from collections import namedtuple
Point = namedtuple('Point', ['x', 'y'])
p = Point(1, 2)
p.x # = 1
p.y # = 2
#################################### deque ####################################
from collections import deque
q = deque(['a', 'b', 'c'])
q.append('x')
q.appendleft('y')
q.pop()
q.popleft()
################################# defaultdict #################################
from collections import defaultdict
dd = defaultdict(lambda: 'N/A')
dd['key1'] = 'abc'
dd['key1'] # = 'abc'
dd['key2'] # = 'N/A'
################################# OrderedDict #################################
from collections import OrderedDict
od = OrderedDict()
od['z'] = 1
od['y'] = 2
od['x'] = 3
list(od.keys()) # ['z', 'y', 'x']
################################### Counter ###################################
from collections import Counter
c = Counter()
for ch in 'programming':
c[ch] = c[ch] + 1
#################################### base64 ####################################
import base64
base64.b64encode(b'binary\x00string')
# b'YmluYXJ5AHN0cmluZw=='
base64.b64decode(b'YmluYXJ5AHN0cmluZw==')
# b'binary\x00string'
base64.urlsafe_b64encode(b'i\xb7\x1d\xfb\xef\xff')
base64.urlsafe_b64decode('abcd--__')
################################# binary pack #################################
import struct
struct.pack('>I', 10240099) # '>' for big-endian, 'I' for 4-byte int
struct.unpack('>IH', b'\xf0\xf0\xf0\xf0\x80\x80')
# (4042322160, 32896)
struct.unpack('<ccIIIIIIHH', bmp_header)
##################################### Hash #####################################
import hashlib
md5 = hashlib.md5() # or hashlib.sha1()
md5.update('how to use md5 in '.encode('utf-8'))
md5.update('python hashlib?'.encode('utf-8'))
print(md5.hexdigest())
################################## itertools ##################################
import itertools
itertools.count(1) # 1 2 3 4 5 ...
itertools.cycle('ABC') # A B C A B ...
itertools.repeat('A') # A A A A A...
itertools.repeat('A', 3) # A A A [end]
natuals = itertools.count(1)
ns = itertools.takewhile(lambda x: x <= 10, natuals)
list(ns) # [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
itertools.chain('ABC', 'XYZ')
itertools.groupby('AAABBBCCAAA') # (key, group)
itertools.groupby('AaaBBbcCAAa', lambda c: c.upper())
A ['A', 'a', 'a']
B ['B', 'B', 'b']
C ['c', 'C']
A ['A', 'A', 'a']
################################ Web operation ################################
from urllib import request
req = request.Request('http://www.douban.com/')
req.add_header('User-Agent', 'Mozilla/6.0 (iPhone; CPU iPhone OS 8_0 like Mac OS X) AppleWebKit/536.26 (KHTML, like Gecko) Version/8.0 Mobile/10A5376e Safari/8536.25')
with request.urlopen(req) as f:
print('Status:', f.status, f.reason)
for k, v in f.getheaders():
print('%s: %s' % (k, v))
print('Data:', f.read().decode('utf-8'))
from urllib import request, parse
print('Login to weibo.cn...')
email = input('Email: ')
passwd = input('Password: ')
login_data = parse.urlencode([
('username', email),
('password', passwd),
('entry', 'mweibo'),
('client_id', ''),
('savestate', '1'),
('ec', ''),
('pagerefer', 'https://passport.weibo.cn/signin/welcome?entry=mweibo&r=http%3A%2F%2Fm.weibo.cn%2F')
])
req = request.Request('https://passport.weibo.cn/sso/login')
req.add_header('Origin', 'https://passport.weibo.cn')
req.add_header('User-Agent', 'Mozilla/6.0 (iPhone; CPU iPhone OS 8_0 like Mac OS X) AppleWebKit/536.26 (KHTML, like Gecko) Version/8.0 Mobile/10A5376e Safari/8536.25')
req.add_header('Referer', 'https://passport.weibo.cn/signin/login?entry=mweibo&res=wel&wm=3349&r=http%3A%2F%2Fm.weibo.cn%2F')
with request.urlopen(req, data=login_data.encode('utf-8')) as f:
print('Status:', f.status, f.reason)
for k, v in f.getheaders():
print('%s: %s' % (k, v))
print('Data:', f.read().decode('utf-8'))
########################## From Iterator to Coroutine ##########################
def consumer():
r = ''
while True:
n = yield r
if not n:
return
print('[CONSUMER] Consuming %s...' % n)
r = '200 OK'
def produce(c):
c.send(None)
n = 0
while n < 5:
n = n + 1
print('[PRODUCER] Producing %s...' % n)
r = c.send(n)
print('[PRODUCER] Consumer return: %s' % r)
c.close()
c = consumer()
produce(c)
################################## Coroutine ##################################
import asyncio
@asyncio.coroutine
def hello():
print("Hello world!")
# call asyncio.sleep(1) asynchronously
r = yield from asyncio.sleep(1)
print("Hello again!")
# Get EventLoop
loop = asyncio.get_event_loop()
# Run coroutine
loop.run_until_complete(hello())
loop.close()
# in python 3.5
async def hello():
print("Hello world!")
# call asyncio.sleep(1) asynchronously
r = await asyncio.sleep(1)
print("Hello again!")
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