$ pip install virtualenv
$ virtualenv myproject

$ source myproject/bin/activate
$ deactivate

virtualenv --system-site-packages mycoolproject

$ python -m pdb my_script.py

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

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 ... ...

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.

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')

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

#(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

def add(value1,value2):
    global result
    result = value1 + value2
add(3,5)
print(result)
# Output: 8

def profile():
    name = "Danny"
    age = 30
    return (name, age)
profile_data = profile()
print(profile_data[0])
# Output: Danny
print(profile_data[1])
# Output: 30

# 更常见的方式：也是返回元组，只不过省略了括号
def profile():
    name = "Danny"
    age = 30
    return name, age

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

# 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

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!')

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

1. Python解释器遇到了yield关键字。因为这个缘故它创建了一个生成器而不是一个普通的函数。
2. 因为这个装饰器，contextmanager会被调用并传入函数名（open_file）作为参数。
3. contextmanager函数返回一个以GeneratorContextManager对象封装过的生成器。
4. 这个GeneratorContextManager被赋值给open_file函数，我们实际上是在调用GeneratorContextManager对象。

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

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')

add = lambda x, y: x + y
print(add(3, 5))
# Output: 8

# 列表排序
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)]

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

number_list = range(-5, 5)
less_than_zero = filter(lambda x: x < 0, number_list)
print(list(less_than_zero))  
# 译者注：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

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}

#dict键值互换
{v: k for k, v in some_dict.items()}

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

def generator_function():
    for i in range(10):
        yield i
for item in generator_function():
    print(item)
# Output: 0
# 1
# 2
...
# 9

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()

class SuperClass(object):
    pi = 3.14
    superpowers = []

    def __init__(self, name):
        self.name = name

    def add_superpower(self, power):
        self.superpowers.append(power)

foo = SuperClass('foo')
bar = SuperClass('bar')
foo.name
# Output: 'foo'

bar.name
# Output: 'bar'


foo.add_superpower('fly')
bar.superpowers
# Output: ['fly']

foo.superpowers
# Output: ['fly']
foo.pi
# 3.14
bar.pi
# 3.14
foo.pi = 300
foo.pi
# 300
bar.pi
# 3.14s

class GetTest(object):
    def __init__(self):
        self.info = {
            'name':'Yasoob',
            'country':'Pakistan',
            'number':12345812
        }

    def __getitem__(self,i):
        return self.info[i]

foo = GetTest()

foo['name']
# Output: 'Yasoob'

foo['number']
# Output: 12345812

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']
# })

#问题
some_dict = {}
some_dict['colours']['favourite'] = "yellow"
##异常输出：KeyError: 'colours'

#解决方案
import collections
tree = lambda: collections.defaultdict(tree)
some_dict = tree()
some_dict['colours']['favourite'] = "yellow"
##运行正常

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
##  })

from collections import 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])

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'
print(perry[0])
## 输出: 'perry'

from collections import namedtuple
from enum import Enum
class Species(Enum):
    cat = 1
    dog = 2
    horse = 3

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)

#有三种方法访问枚举数据，例如以下方法都可以获取到’cat’的值：
Species(1)
Species['cat']
Species.cat

foo = ['hi']
print(foo)
# Output: ['hi']
bar = foo
bar += ['bye']
print(foo)
# 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(element, target=None):
    if target is None:
        target = []
    target.append(element)
    return target

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

@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:
a_function_requiring_decoration = a_new_decorator(a_function_requiring_decoration)

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 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

# 日志装饰器类
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(email_logit, self).__init__(*args, **kwargs)
    def notify(self):
        # 发送一封email到self.email
        pass

#py3.2+ 新特性
from functools import lru_cache
#maxsize描述lru_cache最多缓存最近多少个返回值。

@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]


#清空缓存
fib.cache_clear()

#py2 手动通过装饰器实现该功能
from functools import wraps

def memoize(function):
    memo = {}
    @wraps(function)
    def wrapper(*args):
        try:
            return memo[args]
        except KeyError:
            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)

* 起server
#Python 2
python -m SimpleHTTPServer
#Python 3
python -m http.server

* 漂亮的打印
from pprint import pprint
my_dict = {'name': 'Yasoob', 'age': 'undefined', 'personality': 'awesome'}
pprint(my_dict)

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