Python高级特性_python 3.10新特性

call by object(call by object reference or call by sharing)

# 1
def clear_list(l):
    l = []
ll = [1,2,3]
clear_list(ll)
print(ll)

# 2
def fl(l=[1]):
    l.append(1)
    print(l)
fl()
fl()
# 记住：默认参数只计算一次

# 第一种
foo(1,2,3)
foo(a=1,b=2)

# 第二种
foo(*[1,2,3])
foo(**dict(a=1,b=2)})

def test_var_args(f_arg, *argv):
    print("first normal arg:", f_arg)
    for arg in argv:
        print("another arg through *argv:", arg)

test_var_args('yasoob', 'python', 'eggs', 'test')

first normal arg: yasoob
another arg through *argv: python
another arg through *argv: eggs
another arg through *argv: test

def greet_me(**kwargs):
    for key, value in kwargs.items():
        print("{0} == {1}".format(key, value))

>>> greet_me(name="yasoob")
name == yasoob

def test_args_kwargs(arg1, arg2, arg3):
    print("arg1:", arg1)
    print("arg2:", arg2)
    print("arg3:", arg3)

# 首先使用 *args
>>> args = ("two", 3, 5)
>>> test_args_kwargs(*args)
arg1: two
arg2: 3
arg3: 5

# 现在使用 **kwargs:
>>> kwargs = {"arg3": 3, "arg2": "two", "arg1": 5}
>>> test_args_kwargs(**kwargs)
arg1: 5
arg2: two
arg3: 3

some_func(fargs, *args, **kwargs)

import someclass

def get_info(self, *args):
    return "Test data"

someclass.get_info = get_info

from functools import wraps

def cache(func):
    store = {}
    @wraps(func)
    def _(n):
        if n in store:
            return store[n]
        else:
            res = func(n)
            store[n] = res
            return res
    return _

@cache
def f(n):
    if n <= 1:
        return 1
    return f(n-1) + f(n-2)

>>>def addx(x):
>>>    def adder(y): return x + y
>>>    return adder
>>> c =  addx(8)
>>> type(c)
<type 'function'>
>>> c.__name__
'adder'
>>> c(10)
18

class Person(object):
    def __init__(self, name, age):
        self.name = name
        self.age = age
    def print_name(self):
        print self.name

class Person(object):
    Country = 'china'
    def __init__(self, name, age):
        self.name = name
        self.age = age

    def print_name(self):
        print self.name

    @classmethod
    def print_country(cls):
        print(cls.Country)

    @staticmethod
    def join_name(first_name, last_name):
        return last_name + first_name

# 元类继承自type
class LowercaseMeta(type):
    """ 修改类的书写名称为小写的元类"""
    def __new__(mcs, name, bases, attrs):
        lower_attrs = {}
        for k, v in attrs.items():
            if not k.startswith('__'):
                lower_attrs[k.lower()] = v
            else:
                lower_attr[k] =v
        return type.__new__(mcs, name, bases, lower_attrs)

class LowercaseClass(metaclass=LowercaseMeta):
    BAR = True

    def Hello(self):
        print('hello')

print(dir(LowercaseClass))

LowercaseClass().hello()

$ python -m pdb my_script.py

import pdb

def make_bread():
    pdb.set_trace()
    return "I don't have time"

print(make_bread())

>>> x = [1, 2, 3]
>>> y = iter(x)
>>> next(y)
1
>>> next(y)
2
>>> type(x)
<class 'list'>
>>> type(y)
<class 'list_iterator'>

# content of test.py
def fib(n):
    prev, curr = 0, 1
    while n > 0:
        yield curr
        prev, curr = curr, curr + prev
        n -= 1

>>> from test import fib
>>> y = fib(10)
>>> next(y)
1
>>> type(y)
<class 'generator'>
>>> next(y)
1
>>> next(y)
2

>>> a = (x*x for x in range(10))
>>> a
<generator object <genexpr> at 0x102d79a20>
>>> next(a)
0
>>> next(a)
1
>>> a.close()
>>> next(a)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
StopIteration

>>> def double_inputs():
...     while True:
...         x = yield
...         yield x * 2
...
>>> generator = double_inputs()
>>> generator.send(10)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: can't send non-None value to a just-started generator
>>> generator.send(None)
>>> generator.send(10)
20
>>> next(generator)
>>> generator.send(20)
40

map(function_to_apply, list_of_inputs)

items = [1, 2, 3, 4, 5]
squared = []
for i in items:
    squared.append(i**2)

items = [1, 2, 3, 4, 5]
squared = list(map(lambda x: x**2, items))

def multiply(x):
    return (x*x)
def add(x):
    return (x+x)

funcs = [multiply, add]
for i in range(5):
    value = map(lambda x: x(i), funcs)
    print(list(value))
    # 上面print时，加了list转换，是为了python2/3的兼容性
    # 在python2中map直接返回列表，但在python3中返回迭代器
    # 因此为了兼容python3, 需要list转换一下

# Output:
# [0, 0]
# [1, 2]
# [4, 4]
# [9, 6]
# [16, 8]

number_list = range(-5, 5)
less_than_zero = filter(lambda x: x < 0, number_list)
print(list(less_than_zero))
#          上面print时，加了list转换，是为了python2/3的兼容性
#          在python2中filter直接返回列表，但在python3中返回迭代器
#          因此为了兼容python3, 需要list转换一下
# Output: [-5, -4, -3, -2, -1]

from functools import reduce
product = reduce( (lambda x, y: x * y), [1, 2, 3, 4] )

# Output: 24

some_list = ['a', 'b', 'c', 'b', 'd', 'm', 'n', 'n']

duplicates = []
for value in some_list:
    if some_list.count(value) > 1:
        if value not in duplicates:
            duplicates.append(value)

print(duplicates)
### 输出: ['b', 'n']

some_list = ['a', 'b', 'c', 'b', 'd', 'm', 'n', 'n']
duplicates = set([x for x in some_list if some_list.count(x) > 1])
print(duplicates)
### 输出: set(['b', 'n'])

valid = set(['yellow', 'red', 'blue', 'green', 'black'])
input_set = set(['red', 'brown'])
print(input_set.intersection(valid))
### 输出: set(['red'])

valid = set(['yellow', 'red', 'blue', 'green', 'black'])
input_set = set(['red', 'brown'])
print(input_set.difference(valid))
### 输出: set(['brown'])

a_set = {'red', 'blue', 'green'}
print(type(a_set))
### 输出: <type 'set'>

#如果条件为真，返回真 否则返回假
condition_is_true if condition else condition_is_false

is_fat = True
state = "fat" if is_fat else "not fat"

#(返回假，返回真)[真或假]
(if_test_is_false, if_test_is_true)[test]

fat = True
fitness = ("skinny", "fat")[fat]
print("Ali is ", fitness)
#输出: Ali is fat

condition = True
print(2 if condition else 1/0)
#输出: 2

print((1/0, 2)[condition])
#输出ZeroDivisionError异常

def hi(name="yasoob"):
    return "hi " + name

print(hi())
# output: 'hi yasoob'

# 我们甚⾄可以将⼀个函数赋值给⼀个变量，⽐如
greet = hi
# 我们这⾥没有在使⽤⼩括号，因为我们并不是在调⽤hi函数
# ⽽是在将它放在greet变量⾥头。我们尝试运⾏下这个

print(greet())
# output: 'hi yasoob'

# 如果我们删掉旧的hi函数，看看会发⽣什么！
del hi
print(hi())
#outputs: NameError

print(greet())
#outputs: 'hi yasoob'

def hi(name="yasoob"):
    print("now you are inside the hi() function")

    def greet():
        return "now you are in the greet() function"

    def welcome():
        return "now you are in the welcome() function"

    print(greet())
    print(welcome())
    print("now you are back in the hi() function")

hi()
#output:now you are inside the hi() function
# now you are in the greet() function
# now you are in the welcome() function
# now you are back in the hi() function

# 上面展示了无论何时你调用hi(), greet()和welcome()将会同时被调用。
# 然后greet()和welcome()函数在hi()函数之外是不能访问的，比如：

greet()
#outputs: NameError: name 'greet' is not defined

def hi(name="yasoob"):
    def greet():
        return "now you are in the greet() function"

    def welcome():
        return "now you are in the welcome() function"

    if name == "yasoob":
        return greet
    else:
        return welcome

a = hi()
print(a)
#outputs: <function greet at 0x7f2143c01500>

#上面清晰地展示了`a`现在指向到hi()函数中的greet()函数
#现在试试这个

print(a())
#outputs: now you are in the greet() function

def hi():
    return "hi yasoob!"

def doSomethingBeforeHi(func):
    print("I am doing some boring work before executing hi()")
    print(func())

doSomethingBeforeHi(hi)
#outputs:I am doing some boring work before executing hi()
# hi yasoob!

def a_new_decorator(a_func):
    def wrapTheFunction():
        print("I am doing some boring work before executing a_func()"
        a_func()
        print("I am doing some boring work after executing a_func()"
    return wrapTheFunction

def a_function_requiring_decoration():
    print("I am the function which needs some decoration to remove my foul smell"

a_function_requiring_decoration()
#outputs: "I am the function which needs some decoration to remove my foul smell"

a_function_requiring_decoration = a_new_decorator(a_function_requiring_decoration)
#now a_function_requiring_decoration is wrapped by wrapTheFunction()

a_function_requiring_decoration()
#outputs:I am doing some boring work before executing a_func()
#     I am the function which needs some decoration to remove my foul smell
#     I am doing some boring work after executing a_func()

@a_new_decorator
def a_function_requiring_decoration():
    """Hey you! Decorate me!"""
    print("I am the function which needs some decoration to "
        "remove my foul smell")

a_function_requiring_decoration()
#outputs: I am doing some boring work before executing a_func()
#     I am the function which needs some decoration to remove my foul smell
#     I am doing some boring work after executing a_func()
#the @a_new_decorator is just a short way of saying:

print(a_function_requiring_decoration.__name__)
#     Output: wrapTheFunction

from functools import wraps
def a_new_decorator(a_func):
    @wraps(a_func)
    def wrapTheFunction():
        print("I am doing some boring work before executing a_func()"
        a_func()
        print("I am doing some boring work after executing a_func()"
    return wrapTheFunction

@a_new_decorator
def a_function_requiring_decoration():
    """Hey yo! Decorate me!"""
    print("I am the function which needs some decoration to "
          "remove my foul smell")

print(a_function_requiring_decoration.__name__)
# Output: a_function_requiring_decoration

from functools import wraps
def decorator_name(f):
    @wraps(f)
    def decorated(*args, **kwargs):
        if not can_run:
            return "Function will not run"
        return f(*args, **kwargs)
    return decorated

@decorator_name
def func():
    return("Function is running")

can_run = True
print(func())
# Output: Function is running

can_run = False
print(func())
# Output: Function will not run

import time
def log_time(func): # 接受一个函数作为参数
    def _log(*args, **kwargs):
        beg = time.time()
        res = func(*args, **kwargs)
        print('use time: {}'.format(time.time()-beg))
        return res
    return _log

@log_time   # 装饰器语法糖
def mysleep():
    time.sleep(1)

mysleep()

# 另一种写法

def mysleep2():
    time.sleep(1)

newsleep = log_time(mysleep2)
newsleep()

import time
class LogTime:
    def __call__(self, func): # 接受一个函数作为参数
        def _log(*args, **kwargs):
            beg = time.time()
            res = func(*args, **kwargs)
            print('use time: {}'.format(time.time()-beg))
            return res
        return _log

@LogTime()
def mysleep():
    time.sleep(1)

mysleep()

import time
class LogTime:
    def __init__(self, use_int=False):
        self.use_int = use_int

    def __call__(self, func): # 接受一个函数作为参数
        def _log(*args, **kwargs):
            beg = time.time()
            res = func(*args, **kwargs)
            if self.use_int:
                print('use time: {}'.format(int(time.time()-beg)))
            else:
                print('use time: {}'.format(time.time()-beg))
            return res
        return _log

@LogTime(True)
def mysleep():
    time.sleep(1)

mysleep()

def my_logging(func):

    def wrapper():
        print("{} is running.".format(func.__name__))
        return func()
    return wrapper

@my_logging
def foo():
    print("this is foo function.")

foo()

def my_logging(func):

    def wrapper(*args, **kwargs):
        print("{} is running.".format(func.__name__))
        return func(*args, **kwargs)
    return wrapper

@my_logging
def foo(x, y):
    print("this is foo function.")
    return x + y

print(foo(1, 2))

def my_logging(level):
    def decorator(func):
        def wrapper(*args, **kwargs):
            if level == "info":
                print("{} is running. level: ".format(func.__name__), level)
            elif level == "warn":
                print("{} is running. level: ".format(func.__name__), level)
            return func(*args, **kwargs)
        return wrapper
    return decorator

@my_logging(level="info")
def foo(name="foo"):
    print("{} is running".format(name))

@my_logging(level="warn")
def bar(name="bar"):
    print("{} is running".format(name))

foo()
bar()

class MyLogging(object):

    def __init__(self, func):
        self._func = func

    def __call__(self, *args, **kwargs):
        print("class decorator starting.")
        a = self._func(*args, **kwargs)
        print("class decorator end.")
        return a

@MyLogging
def foo(x, y):
    print("foo is running")
    return x + y

print(foo(1, 2))

from functools import wraps

def requires_auth(f):
    @wraps(f)
    def decorated(*args, **kwargs):
        auth = request.authorization
        if not auth or not check_auth(auth.username, auth.password):
            authenticate()
        return f(*args, **kwargs)
    return decorated

from functools import wraps
def logit(func):
    @wraps(func)
    def with_logging(*args, **kwargs):
        print(func.__name__ + " was called")
        return func(*args, **kwargs)
    return with_logging

@logit
def addition_func(x):
    """Do some math."""
    return x + x

result = addition_func(4)
# Output: addition_func was called

from functools import wraps

def logit(logfile='out.log'):
    def logging_decorator(func):
        @wraps(func)
        def wrapped_function(*args, **kwargs):
            log_string = func.__name__ + " was called"
            print(log_string)
            # 打开logfile，并写⼊内容
            with open(logfile, 'a') as opened_file:
                # 现在将⽇志打到指定的logfile
                opened_file.write(log_string + '\n')
            return func(*args, **kwargs)
        return wrapped_function
    return logging_decorator

@logit()
def myfunc1():
    pass

myfunc1()
# Output: myfunc1 was called
# 现在⼀个叫做 out.log 的⽂件出现了，⾥⾯的内容就是上⾯的字符串

@logit(logfile='func2.log')
def myfunc2():
    pass

myfunc2()
# Output: myfunc2 was called
# 现在⼀个叫做 func2.log 的⽂件出现了，⾥⾯的内容就是上⾯的字符串

from functools import wraps
class logit(object):
    def __init__(self, logfile='out.log'):
        self.logfile = logfile

    def __call__(self, func):
        @wraps(func)
        def wrapped_function(*args, **kwargs):
            log_string = func.__name__ + " was called"
            print(log_string)
            # 打开logfile并写⼊
            with open(self.logfile, 'a') as opened_file:
                # 现在将⽇志打到指定的⽂件
                opened_file.write(log_string + '\n')
            # 现在，发送⼀个通知
            self.notify()
            return func(*args, **kwargs)
        return wrapped_function

def notify(self):
    # logit只打⽇志，不做别的
    pass

@logit() 
def myfunc1():
    Pass

class email_logit(logit):
    '''
    一个logit的实现版本，可以在函数调用时发送email给管理员
    '''
    def __init__(self, email='admin@myproject.com', *args, **kwargs)
        self.email = email
        super(logit, self).__init__(*args, **kwargs)
    
    def notify(self):
        # 发送一封email到self.email
        # 这⾥就不做实现了
        pass

def add(value1, value2):
    return value1 + value2

result = add(3, 5)
print(result)
# Output: 8

def add(value1,value2):
    global result
    result = value1 + value2

add(3,5)
print(result)
# Output: 8

# 首先，是没有使用global变量
def add(value1, value2):
    result = value1 + value2

add(2, 4)
print(result)

# Oh 糟了，我们遇到异常了。为什么会这样？
# python解释器报错说没有一个叫result的变量。
# 这是因为result变量只能在创建它的函数内部才允许访问，除非它是全局的(global)。
Traceback (most recent call last):
    File "", line 1, in
        result
NameError: name 'result' is not defined

# 现在我们运行相同的代码，不过是在将result变量设为global之后
def add(value1, value2):
    global result
    result = value1 + value2

add(2, 4)
print(result)
6

def profile():
    global name
    global age
    name = "Danny"
    age = 30

profile()
print(name)
# Output: Danny

print(age)
# Output: 30

def profile():
    name = "Danny"
    age = 30
    return (name, age)

profile_data = profile()
print(profile_data[0])
# Output: Danny

print(profile_data[1])
# Output: 30

def profile():
    name = "Danny"
    age = 30
    return name, age

foo = ['hi']
print(foo)
# Output: ['hi']

bar = foo
bar += ['bye']
print(foo)
# Output: ['hi', 'bye']

foo = ['hi']
print(foo)
# Output: ['hi']

bar = foo
bar += ['bye']

print(foo)
# Output: ['hi']

print(bar)
# Output: ['hi', 'bye']

def add_to(num, target=[]):
    target.append(num)
    return target

add_to(1)
# Output: [1]

add_to(2)
# Output: [1, 2]

add_to(3)
# Output: [1, 2, 3]

def add_to(num, target=[]):
    target.append(num)
    return target

add_to(1)
# Output: [1]

add_to(2)
# Output: [2]

add_to(3)
# Output: [3]

def add_to(element, target=None):
    if target is None:
        target = []
    target.append(element)
    return target

add_to(42)
# Output: [42]

add_to(42)
# Output: [42]

add_to(42)
# Output: [42]

class MyClass(object):
    def __init__(self, name, identifier):
        self.name = name
        self.identifier = identifier
        self.set_up()
    # ...

class MyClass(object):
    __slots__ = ['name', 'identifier']
    def __init__(self, name, identifier):
        self.name = name
        self.identifier = identifier
        self.set_up()
    # ...

Python 3.4.3 (default, Jun 6 2015, 13:32:34)
Type "copyright", "credits" or "license" for more information.

IPython 4.0.0 -- An enhanced Interactive Python.
? -> Introduction and overview of IPython's features.
%quickref -> Quick reference.
help -> Python's own help system.
object? -> Details about 'object', use 'object??' for extra details.

In [1]: import ipython_memory_usage.ipython_memory_usage as imu

In [2]: imu.start_watching_memory()
In [2] used 0.0000 MiB RAM in 5.31s, peaked 0.00 MiB above current, total RAM usage 15.57 MiB

In [3]: %cat slots.py
class MyClass(object):
    __slots__ = ['name', 'identifier']
    def __init__(self, name, identifier):
        self.name = name
        self.identifier = identifier

num = 1024*256
x = [MyClass(1,1) for i in range(num)]
In [3] used 0.2305 MiB RAM in 0.12s, peaked 0.00 MiB above current, total RAM usage 15.80 MiB

In [4]: from slots import *
In [4] used 9.3008 MiB RAM in 0.72s, peaked 0.00 MiB above current, total RAM usage 25.10 MiB

In [5]: %cat noslots.py
class MyClass(object):
    def __init__(self, name, identifier):
        self.name = name
        self.identifier = identifier

num = 1024*256
x = [MyClass(1,1) for i in range(num)]
In [5] used 0.1758 MiB RAM in 0.12s, peaked 0.00 MiB above current, total RAM usage 25.28 MiB

In [6]: from noslots import *
In [6] used 22.6680 MiB RAM in 0.80s, peaked 0.00 MiB above curren

$ pip install virtualenv

$ virtualenv myproject
$ source bin/activate

virtualenv --system-site-packages mycoolproject

$ deactivate

from collections import defaultdict

colours = (
    ('Yasoob', 'Yellow'),
    ('Ali', 'Blue'),
    ('Arham', 'Green'),
    ('Ali', 'Black'),
    ('Yasoob', 'Red'),
    ('Ahmed', 'Silver'),
)

favourite_colours = defaultdict(list)

for name, colour in colours:
    favourite_colours[name].append(colour)

print(favourite_colours)

# defaultdict(<type 'list'>,
#     {'Arham': ['Green'],
#      'Yasoob': ['Yellow', 'Red'],
#      'Ahmed': ['Silver'],
#      'Ali': ['Blue', 'Black']
# })

some_dict = {}
some_dict['colours']['favourite'] = "yellow"

## 异常输出：KeyError: 'colours'

import collections
tree = lambda: collections.defaultdict(tree)
some_dict = tree()
some_dict['colours']['favourite'] = "yellow"

## 运行正常

import json
print(json.dumps(some_dict))

## 输出: {"colours": {"favourite": "yellow"}}

from collections import Counter

colours = (
    ('Yasoob', 'Yellow'),
    ('Ali', 'Blue'),
    ('Arham', 'Green'),
    ('Ali', 'Black'),
    ('Yasoob', 'Red'),
    ('Ahmed', 'Silver'),
)

favs = Counter(name for name, colour in colours)
print(favs)

## 输出:
## Counter({
##     'Yasoob': 2,
##     'Ali': 2,
##     'Arham': 1,
##     'Ahmed': 1
## })

with open('filename', 'rb') as f:
    line_count = Counter(f)
print(line_count)

from collections import deque

d = deque()

d = deque()
d.append('1')
d.append('2')
d.append('3')

print(len(d))
## 输出: 3

print(d[0])
## 输出: '1'

print(d[-1])
## 输出: '3'

d = deque(range(5))
print(len(d))
## 输出: 5

d.popleft()
## 输出: 0

d.pop()
## 输出: 4

print(d)
## 输出: deque([1, 2, 3])

d = deque(maxlen=30)

d = deque([1,2,3,4,5])
d.extendleft([0])
d.extend([6,7,8])
print(d)

## 输出: deque([0, 1, 2, 3, 4, 5, 6, 7, 8])

man = ('Ali', 30)
print(man[0])

## 输出: Ali

from collections import namedtuple

Animal = namedtuple('Animal', 'name age type')
perry = Animal(name="perry", age=31, type="cat")

print(perry)
## 输出: Animal(name='perry', age=31, type='cat')

print(perry.name)
## 输出: 'perry'

from collections import namedtuple

Animal = namedtuple('Animal', 'name age type')
perry = Animal(name="perry", age=31, type="cat")
perry.age = 42

## 输出:
## Traceback (most recent call last):
##     File "", line 1, in
## AttributeError: can't set attribute

from collections import namedtuple

Animal = namedtuple('Animal', 'name age type')
perry = Animal(name="perry", age=31, type="cat")

print(perry[0])
## 输出: perry

from collections import namedtuple

Animal = namedtuple('Animal', 'name age type')
perry = Animal(name="Perry", age=31, type="cat")

print(perry._asdict())
## 输出: OrderedDict([('name', 'Perry'), ('age', 31), ...

from collections import namedtuple
from enum import Enum

class Species(Enum):
    cat = 1
    dog = 2
    horse = 3
    aardvark = 4
    butterfly = 5
    owl = 6
    platypus = 7
    dragon = 8
    unicorn = 9
    # 依次类推

    # 但我们并不想关⼼同⼀物种的年龄，所以我们可以使⽤⼀个别名
    kitten = 1 # (译者注：幼⼩的猫咪)
    puppy = 2 # (译者注：幼⼩的狗狗)

Animal = namedtuple('Animal', 'name age type')
perry = Animal(name="Perry", age=31, type=Species.cat)
drogon = Animal(name="Drogon", age=4, type=Species.dragon)
tom = Animal(name="Tom", age=75, type=Species.cat)
charlie = Animal(name="Charlie", age=2, type=Species.kitten)

>>>charlie.type == tom.type
True
>>> charlie.type
<Species.cat:1>

Species(1)
Species['cat']
Species.cat

for counter, value in enumerate(some_list):
    print(counter, value)

my_list = ['apple', 'banana', 'grapes', 'pear']
for c, value in enumerate(my_list, 1):
    print(c, value)

# 输出:
(1, 'apple')
(2, 'banana')
(3, 'grapes')
(4, 'pear')

my_list = ['apple', 'banana', 'grapes', 'pear']
counter_list = list(enumerate(my_list, 1))
print(counter_list)
# 输出: [(1, 'apple'), (2, 'banana'), (3, 'grapes'), (4, 'pear')]

my_list = [1, 2, 3]
dir(my_list)
# Output: ['__add__', '__class__', '__contains__', '__delattr__', '__delitem__',
# '__delslice__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__',
# '__getitem__', '__getslice__', '__gt__', '__hash__', '__iadd__', '__imul__',
# '__init__', '__iter__', '__le__', '__len__', '__lt__', '__mul__', '__ne__',
# '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__reversed__', '__rmul__',
# '__setattr__', '__setitem__', '__setslice__', '__sizeof__', '__str__',
# '__subclasshook__', 'append', 'count', 'extend', 'index', 'insert', 'pop',
# 'remove', 'reverse', 'sort']

print(type(''))
# Output: <type 'str'>

print(type([]))
# Output: <type 'list'>

print(type({}))
# Output: <type 'dict'>

print(type(dict))
# Output: <type 'type'>

print(type(3))
# Output: <type 'int'>

name = "Yasoob"
print(id(name))
# Output: 139972439030304

import inspect

print(inspect.getmembers(str))
# Output: [('__add__', <slot wrapper '__add__' of ... ...

variable = [out_exp for out_exp in input_list if out_exp == 2]

multiples = [i for i in range(30) if i % 3 is 0]
print(multiples)
# Output: [0, 3, 6, 9, 12, 15, 18, 21, 24, 27]

squared = []
for x in range(10):
    squared.append(x**2)

squared = [x**2 for x in range(10)]

mcase = {'a': 10, 'b': 34, 'A': 7, 'Z': 3}

mcase_frequency = {
    k.lower(): mcase.get(k.lower(), 0) + mcase.get(k.upper(), 0)
    for k in mcase.keys()
}

# mcase_frequency == {'a': 17, 'z': 3, 'b': 34}

{v: k for k, v in some_dict.items()}

squared = {x**2 for x in [1, 1, 2]}
print(squared)
# Output: {1, 4}

try:
    file = open('test.txt', 'rb')
except IOError as e:
    print('An IOError occurred. {}'.format(e.args[-1]))

try:
    file = open('test.txt', 'rb')
except (IOError, EOFError) as e:
    print("An error occurred. {}".format(e.args[-1]))

try:
    file = open('test.txt', 'rb')
except EOFError as e:
    print("An EOF error occurred.")
    raise e
except IOError as e:
    print("An error occurred.")
    raise e

try:
    file = open('test.txt', 'rb')
except Exception:
    # 打印⼀些异常⽇志，如果你想要的话
    raise

try:
    file = open('test.txt', 'rb')
except IOError as e:
    print('An IOError occurred. {}'.format(e.args[-1]))
finally:
    print("This would be printed whether or not an exception occurred!"

# Output: An IOError occurred. No such file or directory
# This would be printed whether or not an exception occurred!

try:
    print('I am sure no exception is going to occur!')
except Exception:
    print('exception')
else:
    # 这⾥的代码只会在try语句⾥没有触发异常时运⾏,
    # 但是这⾥的异常将 *不会* 被捕获
    print('This would only run if no exception occurs. And an error here '
          'would NOT be caught.')
finally:
    print('This would be printed in every case.')

# Output: I am sure no exception is going to occur!
# This would only run if no exception occurs.
# This would be printed in every case.

try:
    # func   # 可能会抛出异常的代码
except (Exception1, Exception2) as e:  # 可以捕获多个异常并处理
    # 异常处理的代码
else:
    # pass  # 异常没有发生的时候代码逻辑
finally:
    pass     # 无论异常有没有发生都会执行的代码，一般处理资源的关闭和释放

lambda 参数:操作（参数）

add = lambda x, y: x + y

print(add(3, 5))
# Output: 8

a = [(1, 2), (4, 1), (9, 10), (13, -3)]
a.sort(key=lambda x: x[1])

print(a)
# Output: [(13, -3), (4, 1), (1, 2), (9, 10)]

data = zip(list1, list2)
data.sort()
list1, list2 = map(lambda t: list(t), zip(*data))

# Python 2
python -m SimpleHTTPServer

# Python 3
python -m http.server

from pprint import pprint

my_dict = {'name': 'Yasoob', 'age': 'undefined'}
pprint(my_dict)

cat file.json | python -m json.tool

python -m cProfile my_script.py

python -c "import csv,json;print json.dumps(list(csv.reader))

a_list = [[1,2],[3,4],[5,6]]

print(list(itertools.chain.from_iterable(a_list)))
# Output: [1, 2, 3, 4, 5, 6]

# or
print(list(itertools.chain(*a_list)))
# Output: [1, 2, 3, 4, 5, 6]

class A(object):
    def __init__(self, a, b, c, d, e, f):
        self.__dict__.update({k: v for k, v in locals().items})

fruits = ['apple', 'banana', 'mango']
for fruit in fruits:
    print(fruit.capitalize())

# Output: Apple
#     Banana
#     Mango

for item in container:
    if search_something(item):
        # Found it!
        process(item)
        break
else:
    # Didn't find anything..
    not_found_in_container()

for n in range(2, 10):
    for x in range(2, n):
        if n % x == 0:
            print(n, 'equals', x, '*', n/x)
            break

for n in range(2, 10):
    for x in range(2, n):
        if n % x == 0:
            print( n, 'equals', x, '*', n/x)
            break
        else:
            # loop fell through without finding a factor
            print(n, 'is a prime number')

//sample C file to add 2 numbers - int and floats
#include <stdio.h>

int add_int(int, int);
float add_float(float, float);

int add_int(int num1, int num2){
    return num1 + num2;
}

float add_float(float num1, float num2){
    return num1 + num2;
}

#For Linux
$ gcc -shared -W1,-soname,adder -o adder.so -fPIC add.c

#For Mac
$ gcc -shared -Wl,-install name,adder,so -o adder.so -fPIC add.c

from ctypes import *

#load the shared object file
adder = CDLL('./adder.so')

#Find sum of integers
res_int = adder.add_int(4,5)
print "Sum of 4 and 5 = " + str(res_int)

#Find sum of floats
a = c_float(5.5)
b = c_float(4.1)

add_float = adder.add_float
add_float.restype = c_float
print "Sum of 5.5 and 4.1 = ", str(add_float(a, b))

Sum of 4 and 5 = 9
Sum of 5.5 and 4.1 = 9.60000038147

/* File : example.c */

#include <time.h>
double My_variable = 3.0;

int fact(int n) {
    if (n <= 1) return 1;
    else return n*fact(n-1);
}

int my_mod(int x, int y) {
    return (x%y);
}
	
char *get_time()
{
    time_t ltime;
    time(<ime);
    return ctime(<ime);
}

unix % swig -python example.i
unix % gcc -c example.c example_wrap.c \
    -I/usr/local/include/python2.1
unix % ld -shared example.o example_wrap.o -o _example.so

>>> import example
>>> example.fact(5)
120

>>> example.my_mod(7,3)
1

>>> example.get_time()
'Sun Feb 11 23:01:07 1996'
>>>

#Though it looks like an ordinary python import, the addList module is implemented in C
import addList
l = [1,2,3,4,5]
print "Sum of List - " + str(l) + " = " + str(addList.add(l))

//Python.h has all the required function definitions to manipulate the Python objects
#include <Python.h>

//This is the function that is called from your python code
static PyObject* addList_add(PyObject* self, PyObject* args){

    PyObject * listObj;

    //The input arguments come as a tuple, we parse the args to get the various variables
    //In this case it's only one list variable, which will now be referenced by listObj
    if (! PyArg_ParseTuple( args, "O", &listObj ))
        return NULL;

    //length of the list
    long length = PyList_Size(listObj);

    //iterate over all the elements
    int i, sum =0;

    for (i = 0; i < length; i++) {
        //get an element out of the list - the element is also a python objects
        PyObject* temp = PyList_GetItem(listObj, i);
        //we know that object represents an integer - so convert it into C long
        long elem = PyInt_AsLong(temp);
        sum += elem;
    }

    //value returned back to python code - another python object
    //build value here converts the C long to a python integer
    return Py_BuildValue("i", sum);
}

//This is the docstring that corresponds to our 'add' function.
static char addList_docs[] = "add( ): add all elements of the list\n";
/* This table contains the relavent info mapping -
<function-name in python module>, <actual-function>,
<type-of-args the function expects>, <docstring associated with the function>
*/

static PyMethodDef addList_funcs[] = {
    {"add", (PyCFunction)addList_add, METH_VARARGS, addList_docs},
    {NULL, NULL, 0, NULL}
};

/*
    addList is the module name, and this is the initialization block of the module.
    <desired module name>, <the-info-table>, <module's-docstring>
*/

PyMODINIT_FUNC initaddList(void){
    Py_InitModule3("addList", addList_funcs, "Add all ze lists");
}

int n;
char *s;
PyObject* list;
PyArg_ParseTuple(args, "siO", &n, &s, &list);

#build the modules

from distutils.core import setup, Extension

setup(name='addList', version='1.0', \
    ext_modules=[Extension('addList', ['adder.c'])])

python setup.py install

#module that talks to the C code
import addList

l = [1,2,3,4,5]
print "Sum of List - " + str(l) + " = " + str(addList.add(l))

Sum of List - [1,2,3,4,5] = 15

#! /usr/bin/python
 
from threading import Thread
import time
 
def my_counter():
    i = 0
    for _ in range(100000000):
        i = i + 1
    return True
 
def main():
    thread_array = {}
    start_time = time.time()
    for tid in range(2):
        t = Thread(target=my_counter)
        t.start()
        t.join()
    end_time = time.time()
    print("Total time: {}".format(end_time - start_time))
 
if __name__ == '__main__':
    main()

#! /usr/bin/python
 
from threading import Thread
import time
 
def my_counter():
    i = 0
    for _ in range(100000000):
        i = i + 1
    return True
 
def main():
    thread_array = {}
    start_time = time.time()
    for tid in range(2):
        t = Thread(target=my_counter)
        t.start()
        thread_array[tid] = t
    for i in range(2):
        thread_array[i].join()
    end_time = time.time()
    print("Total time: {}".format(end_time - start_time))
 
if __name__ == '__main__':
    main()

while True:
    acquire GIL
    for i in 1000:
        do something
    release GIL
    /* Give Operating System a chance to do thread scheduling */

f = open('photo.jpg', 'r+')
jpgdata = f.read()
f.close()

with open('photo.jpg', 'r+') as f:
    jpgdata = f.read()

import io
with open('photo.jpg', 'rb') as inf:
    jpgdata = inf.read()

if jpgdata.startswith(b'\xff\xd8'):
    text = u'This is a JPEG file (%d bytes long)\n'
else:
    text = u'This is a random file (%d bytes long)\n'

with io.open('summary.txt', 'w', encoding='utf-8') as outf:
    outf.write(text % len(jpgdata))

from __future__ import with_statement

print
# Output:

from __future__ import print_function
print(print)
# Output: <built-in function print>

import foo
# or
from foo import bar

import foo as foo

try:
    import urllib.request as urllib_request # for Python 3
except ImportError:
    import urllib2 as urllib_request # for Python 2

from future.builtins.disabled import *

from future.builtins.disabled import *

apply()
# Output: NameError: obsolete Python 2 builtin apply is disabled

def fib():
    a, b = 0, 1
    while True:
        yield a
        a, b = b, a+b

for i in fib():
    print i

def grep(pattern):
    print("Searching for", pattern)
    while True:
        line = (yield)
        if pattern in line:
            print(line)

search = grep('coroutine')
next(search)
#output: Searching for coroutine
search.send("I love you")
search.send("Don't you love me?")
search.send("I love coroutine instead!")
#output: I love coroutine instead!

search = grep('coroutine')
search.close()

from functools import lru_cache

@lru_cache(maxsize=32)
def fib(n):
    if n < 2:
        return n
    return fib(n-1) + fib(n-2)

>>> print([fib(n) for n in range(10)])
# Output: [0, 1, 1, 2, 3, 5, 8, 13, 21, 34]

fib.cache_clear()

from functools import wraps

def memoize(function):
    memo = {}
    @wraps(function)
    def wrapper(*args):
        if args in memo:
            return memo[args]
        else:
            rv = function(*args)
            memo[args] = rv
            return rv
    return wrapper

@memoize
def fibonacci(n):
    if n < 2: return n
    return fibonacci(n - 1) + fibonacci(n - 2)

fibonacci(25)

with open('some_file', 'w') as opened_file:
    opened_file.write('Hola!')

file = open('some_file', 'w')
try:
    file.write('Hola!')
finally:
    file.close()

class File(object):
    def __init__(self, file_name, method):
        self.file_obj = open(file_name, method)
    def __enter__(self):
        return self.file_obj
    def __exit__(self, type, value, traceback):
        self.file_obj.close()

with File('demo.txt', 'w') as opened_file:
    opened_file.write('Hola!')

with File('demo.txt', 'w') as opened_file:
    opened_file.undefined_function('Hola!')

Traceback (most recent call last):
    File "<stdin>", line 2, in <module>
AttributeError: 'file' object has no attribute 'undefined_function'

class File(object):
    def __init__(self, file_name, method):
        self.file_obj = open(file_name, method)
    def __enter__(self):
        return self.file_obj
    def __exit__(self, type, value, traceback):
        print("Exception has been handled")
        self.file_obj.close()
        return True

with File('demo.txt', 'w') as opened_file:
    opened_file.undefined_function()

# Output: Exception has been handled

from contextlib import contextmanager

@contextmanager
def open_file(name):
    f = open(name, 'w')
    yield f
    f.close()

with open_file('some_file') as f:
    f.write('hola!')