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'''这是一段多行字符串。这是它的第一行。
This is the second line.
"What's your name?," I asked.
He said "Bond, James Bond."
'''

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# 字符串替换相应格式，Python从0开始计数
age = 20
name = 'Swaroop'
print('{0} was {1} years old when he wrote this book'.format(name, age))
print('Why is {0} playing with that python?'.format(name))

# 数字只是一个可选选项，所以你同样可以写成
age = 20
name = 'Swaroop'
print('{} was {} years old when he wrote this book'.format(name, age))
print('Why is {} playing with that python?'.format(name))

# 对于浮点数 '0.333' 保留小数点(.)后三位
print('{0:.3f}'.format(1.0/3))

# 使用下划线填充文本，并保持文字处于中间位置
# 使用 (^) 定义 '___hello___'字符串长度为 11
print('{0:_^11}'.format('hello'))

# 基于关键词输出 'Swaroop wrote A Byte of Python'
print('{name} wrote {book}'.format(name='Swaroop', book='A Byte of Python'))

# 注意 print 总是会以一个不可见的“新一行”字符（\n）结尾，因此重复调用 print将会在相互独立的一行中分别打印。
# 为防止打印过程中出现这一换行符，你可以通过 end 指定其应以空白结尾，输出结果为 "ab"
print('a', end='')
print('b', end='')

# 或者你通过 end 指定以空格结尾，输出结果为“a b c”
print('a', end=' ')
print('b', end=' ')
print('c')

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#  相当于"This is the first sentence. This is the second sentence."
"This is the first sentence. \
This is the second sentence."

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# 输出为This is a string. This continues the string.
s = 'This is a string. \
This continues the string.'
print(s)

# 等同于 i = 5
i = \
5

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i = 5
# 下面将发生错误，注意行首有一个空格
 print('Value is', i)
print('I repeat, the value is', i)

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  File "whitespace.py", line 3
    print('Value is', i)
    ^
IndentationError: unexpected indent
# 缩进错误：意外缩进

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number = 23
guess = int(input('Enter an integer : '))

if guess == number:
    # 新块从这里开始
    print('Congratulations, you guessed it.')
    print('(but you do not win any prizes!)')
    # 新块在这里结束
elif guess < number:
    # 另一代码块
    print('No, it is a little higher than that')
    # 你可以在此做任何你希望在该代码块内进行的事情
else:
    print('No, it is a little lower than that')
    # 你必须通过猜测一个大于（>）设置数的数字来到达这里。

print('Done')
# 这最后一句语句将在
# if 语句执行完毕后执行。

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number = 23
running = True

while running:
    # 通过 input() 函数来获取用户的猜测数
    guess = int(input('Enter an integer : '))

    if guess == number:
        print('Congratulations, you guessed it.')
        # 这将导致 while 循环中止
        running = False
    elif guess < number:
        print('No, it is a little higher than that.')
    else:
        print('No, it is a little lower than that.')
else:
    print('The while loop is over.')
    # 在这里你可以做你想做的任何事

print('Done')

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# 通过内置的 range 函数生成这一数字序列
# range(1,5) 将输出序列 [1, 2, 3, 4]
for i in range(1, 5):
    print(i)
else:
    print('The for loop is over')

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while True:
    s = input('Enter something : ')
    if s == 'quit':
        break
    print('Length of the string is', len(s))
print('Done')

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while True:
    s = input('Enter something : ')
    if s == 'quit':
        break
    if len(s) < 3:
        print('Too small')
        continue
    print('Input is of sufficient length')
    # 自此处起继续进行其它任何处理

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def print_max(a, b):
    # 该块属于这一函数
    if a > b:
        print(a, 'is maximum')
    elif a == b:
        print(a, 'is equal to', b)
    else:
        print(b, 'is maximum')
# 函数结束

# 直接传递字面值
print_max(3, 4) # 调用函数

x = 5
y = 7

# 以参数的形式传递变量
print_max(x, y)

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x = 50

def func(x):
    print('x is', x)
    x = 2
    print('Changed local x to', x)

func(x)
print('x is still', x)

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$ python function_local.py
x is 50
Changed local x to 2
x is still 50

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x = 50

def func():
    global x

    print('x is', x)
    x = 2
    print('Changed global x to', x)

func()
print('Value of x is', x)

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$ python function_global.py
x is 50
Changed global x to 2
Value of x is 2

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def say(message, times=1):
    print(message * times)

say('Hello')
say('World', 5)

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$ python function_default.py
Hello
WorldWorldWorldWorldWorld

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def func(a, b=5, c=10):
    print('a is', a, 'and b is', b, 'and c is', c)

func(3, 7)
func(25, c=24)
func(c=50, a=100)

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$ python function_keyword.py
a is 3 and b is 7 and c is 10
a is 25 and b is 5 and c is 24
a is 100 and b is 5 and c is 50

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def total(a=5, *numbers, **phonebook):
    print('a', a)

    #遍历元组中的所有项目
    for single_item in numbers:
        print('single_item', single_item)

    #遍历字典中的所有项目
    for first_part, second_part in phonebook.items():
        print(first_part,second_part)

print(total(10,1,2,3,Jack=1123,John=2231,Inge=1560))

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$ python function_varargs.py
a 10
single_item 1
single_item 2
single_item 3
Inge 1560
John 2231
Jack 1123
None

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def maximum(x, y):
    if x > y:
        return x
    elif x == y:
        return 'The numbers are equal'
    else:
        return y

print(maximum(2, 3))

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$ python function_return.py
3

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def some_function():
    pass

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def print_max(x, y):
    '''Prints the maximum of two numbers.打印两个数值中的最大数。

    The two values must be integers.这两个数都应该是整数'''
    # 如果可能，将其转换至整数类型
    x = int(x)
    y = int(y)

    if x > y:
        print(x, 'is maximum')
    else:
        print(y, 'is maximum')

print_max(3, 5)
print(print_max.__doc__)

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$ python function_docstring.py
5 is maximum
Prints the maximum of two numbers.

    The two values must be integers.

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import sys

print('The command line arguments are:')
for i in sys.argv:
    print(i)

print('\n\nThe PYTHONPATH is', sys.path, '\n')

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$ python module_using_sys.py we are arguments
The command line arguments are:
module_using_sys.py
we
are
arguments


The PYTHONPATH is ['/tmp/py',
# many entries here, not shown here
'/Library/Python/2.7/site-packages',
'/usr/local/lib/python2.7/site-packages']

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from math import sqrt
print("Square root of 16 is", sqrt(16))

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if __name__ == '__main__':
    print('This program is being run by itself')
else:
    print('I am being imported from another module')

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$ python module_using_name.py
This program is being run by itself

$ python
>>> import module_using_name
I am being imported from another module
>>>

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def say_hi():
    print('Hi, this is mymodule speaking.')

__version__ = '0.1'

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import mymodule

mymodule.say_hi()
print('Version', mymodule.__version__)

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$ python mymodule_demo.py
Hi, this is mymodule speaking.
Version 0.1

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from mymodule import say_hi, __version__

say_hi()
print('Version', __version__)

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from mymodule import *

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$ python
>>> import sys

# 给出 sys 模块中的属性名称
>>> dir(sys)
['__displayhook__', '__doc__',
'argv', 'builtin_module_names',
'version', 'version_info']
# only few entries shown here

# 给出当前模块的属性名称
>>> dir()
['__builtins__', '__doc__',
'__name__', '__package__']

# 创建一个新的变量 'a'
>>> a = 5

>>> dir()
['__builtins__', '__doc__', '__name__', '__package__', 'a']

# 删除或移除一个名称
>>> del a

>>> dir()
['__builtins__', '__doc__', '__name__', '__package__']

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- <some folder present in the sys.path>/
    - world/
        - __init__.py
        - asia/
            - __init__.py
            - india/
                - __init__.py
                - foo.py
        - africa/
            - __init__.py
            - madagascar/
                - __init__.py
                - bar.py

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# This is my shopping list
shoplist = ['apple', 'mango', 'carrot', 'banana']

print('I have', len(shoplist), 'items to purchase.')

print('These items are:', end=' ')
for item in shoplist:
    print(item, end=' ')

print('\nI also have to buy rice.')
shoplist.append('rice')
print('My shopping list is now', shoplist)

print('I will sort my list now')
shoplist.sort()
print('Sorted shopping list is', shoplist)

print('The first item I will buy is', shoplist[0])
olditem = shoplist[0]
del shoplist[0]
print('I bought the', olditem)
print('My shopping list is now', shoplist)

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$ python ds_using_list.py
I have 4 items to purchase.
These items are: apple mango carrot banana
I also have to buy rice.
My shopping list is now ['apple', 'mango', 'carrot', 'banana', 'rice']
I will sort my list now
Sorted shopping list is ['apple', 'banana', 'carrot', 'mango', 'rice']
The first item I will buy is apple
I bought the apple
My shopping list is now ['banana', 'carrot', 'mango', 'rice']

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# 我会推荐你总是使用括号
# 来指明元组的开始与结束
# 尽管括号是一个可选选项。
# 明了胜过晦涩，显式优于隐式。
zoo = ('python', 'elephant', 'penguin')
print('Number of animals in the zoo is', len(zoo))

new_zoo = 'monkey', 'camel', zoo
print('Number of cages in the new zoo is', len(new_zoo))
print('All animals in new zoo are', new_zoo)
print('Animals brought from old zoo are', new_zoo[2])
print('Last animal brought from old zoo is', new_zoo[2][2])
print('Number of animals in the new zoo is',
      len(new_zoo)-1+len(new_zoo[2]))

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$ python ds_using_tuple.py
Number of animals in the zoo is 3
Number of cages in the new zoo is 3
All animals in new zoo are ('monkey', 'camel', ('python', 'elephant', 'penguin'))
Animals brought from old zoo are ('python', 'elephant', 'penguin')
Last animal brought from old zoo is penguin
Number of animals in the new zoo is 5

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# “ab”是地址（Address）簿（Book）的缩写

ab = {
    'Swaroop': 'swaroop@swaroopch.com',
    'Larry': 'larry@wall.org',
    'Matsumoto': 'matz@ruby-lang.org',
    'Spammer': 'spammer@hotmail.com'
}

print("Swaroop's address is", ab['Swaroop'])

# 删除一对键值—值配对
del ab['Spammer']

print('\nThere are {} contacts in the address-book\n'.format(len(ab)))

for name, address in ab.items():
    print('Contact {} at {}'.format(name, address))

# 添加一对键值—值配对
ab['Guido'] = 'guido@python.org'

if 'Guido' in ab:
    print("\nGuido's address is", ab['Guido'])

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$ python ds_using_dict.py
Swaroop's address is swaroop@swaroopch.com

There are 3 contacts in the address-book

Contact Swaroop at swaroop@swaroopch.com
Contact Matsumoto at matz@ruby-lang.org
Contact Larry at larry@wall.org

Guido's address is guido@python.org

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items = dict.items()
items.sort()
for key,value in items:
   print key, value # print key,dict[key]

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print key, dict[key] for key in sorted(dict.keys())

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#用lambda表达式来排序，更灵活：
sorted(dict.items(), lambda x, y: cmp(x[1], y[1]))
#降序
sorted(dict.items(), lambda x, y: cmp(x[1], y[1]), reverse=True)

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sorted(...)
sorted(iterable, cmp=None, key=None, reverse=False) --> new sorted list

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shoplist = ['apple', 'mango', 'carrot', 'banana']
name = 'swaroop'

# Indexing or 'Subscription' operation #
# 索引或“下标（Subscription）”操作符 #
print('Item 0 is', shoplist[0])
print('Item 1 is', shoplist[1])
print('Item 2 is', shoplist[2])
print('Item 3 is', shoplist[3])
print('Item -1 is', shoplist[-1])
print('Item -2 is', shoplist[-2])
print('Character 0 is', name[0])

# Slicing on a list #
print('Item 1 to 3 is', shoplist[1:3])
print('Item 2 to end is', shoplist[2:])
print('Item 1 to -1 is', shoplist[1:-1])
print('Item start to end is', shoplist[:])

# 从某一字符串中切片 #
print('characters 1 to 3 is', name[1:3])
print('characters 2 to end is', name[2:])
print('characters 1 to -1 is', name[1:-1])
print('characters start to end is', name[:])

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$ python ds_seq.py
Item 0 is apple
Item 1 is mango
Item 2 is carrot
Item 3 is banana
Item -1 is banana
Item -2 is carrot
Character 0 is s
Item 1 to 3 is ['mango', 'carrot']
Item 2 to end is ['carrot', 'banana']
Item 1 to -1 is ['mango', 'carrot']
Item start to end is ['apple', 'mango', 'carrot', 'banana']
characters 1 to 3 is wa
characters 2 to end is aroop
characters 1 to -1 is waroo
characters start to end is swaroop

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>>> shoplist = ['apple', 'mango', 'carrot', 'banana']
>>> shoplist[::1]
['apple', 'mango', 'carrot', 'banana']
>>> shoplist[::2]
['apple', 'carrot']
>>> shoplist[::3]
['apple', 'banana']
>>> shoplist[::-1]
['banana', 'carrot', 'mango', 'apple']

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>>> bri = set(['brazil', 'russia', 'india'])
>>> 'india' in bri
True
>>> 'usa' in bri
False
>>> bric = bri.copy()
>>> bric.add('china')
>>> bric.issuperset(bri)
True
>>> bri.remove('russia')
>>> bri & bric # OR bri.intersection(bric)
{'brazil', 'india'}

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print('Simple Assignment')
shoplist = ['apple', 'mango', 'carrot', 'banana']
# mylist 只是指向同一对象的另一种名称
mylist = shoplist

# 我购买了第一项项目，所以我将其从列表中删除
del shoplist[0]

print('shoplist is', shoplist)
print('mylist is', mylist)
# 注意到 shoplist 和 mylist 二者都
# 打印出了其中都没有 apple 的同样的列表，以此我们确认
# 它们指向的是同一个对象

print('Copy by making a full slice')
# 通过生成一份完整的切片制作一份列表的副本
mylist = shoplist[:]
# 删除第一个项目
del mylist[0]

print('shoplist is', shoplist)
print('mylist is', mylist)
# 注意到现在两份列表已出现不同

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$ python ds_reference.py
Simple Assignment
shoplist is ['mango', 'carrot', 'banana']
mylist is ['mango', 'carrot', 'banana']
Copy by making a full slice
shoplist is ['mango', 'carrot', 'banana']
mylist is ['carrot', 'banana']

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# 这是一个字符串对象
name = 'Swaroop'

if name.startswith('Swa'):
    print('Yes, the string starts with "Swa"')

if 'a' in name:
    print('Yes, it contains the string "a"')

if name.find('war') != -1:
    print('Yes, it contains the string "war"')

delimiter = '_*_'
mylist = ['Brazil', 'Russia', 'India', 'China']
print(delimiter.join(mylist))

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$ python ds_str_methods.py
Yes, the string starts with "Swa"
Yes, it contains the string "a"
Yes, it contains the string "war"
Brazil_*_Russia_*_India_*_China

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#!/usr/bin/env python
# -*- coding: utf_8 -*-
# Date: 2016年10月10日
# Author:蔚蓝行

#首先创建一个类cls,这个类中包含一个值为1的类变量clsvar，一个值为2的实例变量insvar,
class cls:
    clsvar = 1
    def __init__(self):
        self.insvar = 2

#创建类的实例ins1和ins2
ins1 = cls()
ins2 = cls()

#用实例1为类变量重新赋值并打印
print '#'*10
ins1.clsvar = 20
print cls.clsvar     #输出结果为1
print ins1.clsvar    #输出结果为20
print ins2.clsvar    #输出结果为1

#用类名为类变量重新赋值并打印
print '#'*10
cls.clsvar = 10
print cls.clsvar     #输出结果为10
print ins1.clsvar    #输出结果为20
print ins2.clsvar    #输出结果为10

#这次直接给实例1没有在类中定义的变量赋值
print '#'*10
ins1.x = 11
print ins1.x         #输出结果为11

#然后再用类名给类中没有定义的变量赋值
print '#'*10
cls.m = 21
print cls.m          #输出结果为21

#再创建一个实例ins3，然后打印一下ins3的变量
print '#'*10
ins3 = cls()
print ins3.insvar    #输出结果为2
print ins3.clsvar    #输出结果为10
print ins3.m         #输出结果为21
print ins3.x         #报错AttributeError: cls instance has no attribute 'x'

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print cls.__dict__
print ins1.__dict__

########输出#######

{'clsvar': 1, '__module__': '__main__', '__doc__': None, '__init__': <function __init__ at 0x101bbc398>}
{'insvar': 2}

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ins1.clsvar = 20
print ins1.__dict__
print cls.__dict__

########输出#######
{'insvar': 2, 'clsvar': 20}
{'clsvar': 1, '__module__': '__main__', '__doc__': None, '__init__': <function __init__ at 0x10c768398>}

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bokeyuan={"b":1,
       "o":2,
       "k":3,
       "e":4,
       "y":5,
       "u":6,
       "a":7,
       "n":8,     
       }

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class Dict2Obj:
    def __init__(self,bokeyuan):
        self.b = bokeyuan['b']
        self.o = bokeyuan['o']
        self.k = bokeyuan['k']
        self.e = bokeyuan['e']
        self.y = bokeyuan['y']
        self.u = bokeyuan['u']
        self.a = bokeyuan['a']
        self.n = bokeyuan['n']

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class Dict2Obj:
    def __init__(self,bokeyuan):
        self.__dict__.update(bokeyuan)  

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# coding=UTF-8

class SchoolMember:
    '''代表任何学校里的成员。'''
    def __init__(self, name, age):
        self.name = name
        self.age = age
        print('(Initialized SchoolMember: {})'.format(self.name))

    def tell(self):
        '''告诉我有关我的细节。'''
        print('Name:"{}" Age:"{}"'.format(self.name, self.age), end=" ")


class Teacher(SchoolMember):
    '''代表一位老师。'''
    def __init__(self, name, age, salary):
        SchoolMember.__init__(self, name, age)
        self.salary = salary
        print('(Initialized Teacher: {})'.format(self.name))

    def tell(self):
        SchoolMember.tell(self)
        print('Salary: "{:d}"'.format(self.salary))


class Student(SchoolMember):
    '''代表一位学生。'''
    def __init__(self, name, age, marks):
        SchoolMember.__init__(self, name, age)
        self.marks = marks
        print('(Initialized Student: {})'.format(self.name))

    def tell(self):
        SchoolMember.tell(self)
        print('Marks: "{:d}"'.format(self.marks))

t = Teacher('Mrs. Shrividya', 40, 30000)
s = Student('Swaroop', 25, 75)

# 打印一行空白行
print()

members = [t, s]
for member in members:
    # 对全体师生工作
    member.tell()

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$ python oop_subclass.py
(Initialized SchoolMember: Mrs. Shrividya)
(Initialized Teacher: Mrs. Shrividya)
(Initialized SchoolMember: Swaroop)
(Initialized Student: Swaroop)

Name:"Mrs. Shrividya" Age:"40" Salary: "30000"
Name:"Swaroop" Age:"25" Marks: "75"

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def reverse(text):
    return text[::-1]


def is_palindrome(text):
    return text == reverse(text)


something = input("Enter text: ")
if is_palindrome(something):
    print("Yes, it is a palindrome")
else:
    print("No, it is not a palindrome")

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$ python3 io_input.py
Enter text: sir
No, it is not a palindrome

$ python3 io_input.py
Enter text: madam
Yes, it is a palindrome

$ python3 io_input.py
Enter text: racecar
Yes, it is a palindrome

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poem = '''\
Programming is fun
When the work is done
if you wanna make your work also fun:
    use Python!
'''

# 打开文件以编辑（'w'riting）
f = open('poem.txt', 'w')
# 向文件中编写文本
f.write(poem)
# 关闭文件
f.close()

# 如果没有特别指定，
# 将假定启用默认的阅读（'r'ead）模式
f = open('poem.txt')
while True:
    line = f.readline()
    # 零长度指示 EOF
    if len(line) == 0:
        break
    # 每行（`line`）的末尾
    # 都已经有了换行符
    #因为它是从一个文件中进行读取的
    print(line, end='')
# 关闭文件
f.close()

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$ python3 io_using_file.py
Programming is fun
When the work is done
if you wanna make your work also fun:
    use Python!

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import pickle

# The name of the file where we will store the object
shoplistfile = 'shoplist.data'
# The list of things to buy
shoplist = ['apple', 'mango', 'carrot']

# Write to the file
f = open(shoplistfile, 'wb')
# Dump the object to a file
pickle.dump(shoplist, f)
f.close()

# Destroy the shoplist variable
del shoplist

# Read back from the storage
f = open(shoplistfile, 'rb')
# Load the object from the file
storedlist = pickle.load(f)
print(storedlist)

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$ python io_pickle.py
['apple', 'mango', 'carrot']

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>>> "hello world"
'hello world'
>>> type("hello world")
<class 'str'>
>>> u"hello world"
'hello world'
>>> type(u"hello world")
<class 'str'>

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# encoding=utf-8
import io

f = io.open("abc.txt", "wt", encoding="utf-8")
f.write(u"Imagine non-English language here")
f.close()

text = io.open("abc.txt", encoding="utf-8").read()
print(text)

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>>> Print("Hello World")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'Print' is not defined
>>> print("Hello World")
Hello World

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>>> s = input('Enter something --> ')
Enter something --> Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
EOFError

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try:
    text = input('Enter something --> ')
except EOFError:
    print('Why did you do an EOF on me?')
except KeyboardInterrupt:
    print('You cancelled the operation.')
else:
    print('You entered {}'.format(text))

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# Press ctrl + d
$ python exceptions_handle.py
Enter something --> Why did you do an EOF on me?

# Press ctrl + c
$ python exceptions_handle.py
Enter something --> ^CYou cancelled the operation.

$ python exceptions_handle.py
Enter something --> No exceptions
You entered No exceptions

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# encoding=UTF-8

class ShortInputException(Exception):
    '''一个由用户定义的异常类'''
    def __init__(self, length, atleast):
        Exception.__init__(self)
        self.length = length
        self.atleast = atleast

try:
    text = input('Enter something --> ')
    if len(text) < 3:
        raise ShortInputException(len(text), 3)
    # 其他工作能在此处继续正常运行
except EOFError:
    print('Why did you do an EOF on me?')
except ShortInputException as ex:
    print(('ShortInputException: The input was ' +
           '{0} long, expected at least {1}')
          .format(ex.length, ex.atleast))
else:
    print('No exception was raised.')

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$ python exceptions_raise.py
Enter something --> a
ShortInputException: The input was 1 long, expected at least 3

$ python exceptions_raise.py
Enter something --> abc
No exception was raised.

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import sys
import time

f = None
try:
    f = open("poem.txt")
    # 我们常用的文件阅读风格
    while True:
        line = f.readline()
        if len(line) == 0:
            break
        print(line, end='')
        sys.stdout.flush()
        print("Press ctrl+c now")
        # 为了确保它能运行一段时间
        time.sleep(2)
except IOError:
    print("Could not find file poem.txt")
except KeyboardInterrupt:
    print("!! You cancelled the reading from the file.")
finally:
    if f:
        f.close()
    print("(Cleaning up: Closed the file)")

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$ python exceptions_finally.py
Programming is fun
Press ctrl+c now
^C!! You cancelled the reading from the file.
(Cleaning up: Closed the file)

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with open("poem.txt") as f:
    for line in f:
        print(line, end='')

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>>> import sys
>>> sys.version_info
sys.version_info(major=3, minor=5, micro=1, releaselevel='final', serial=0)
>>> sys.version_info.major == 3
True

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import os
import platform
import logging

if platform.platform().startswith('Windows'):
    logging_file = os.path.join(os.getenv('HOMEDRIVE'),
                                os.getenv('HOMEPATH'),
                                'test.log')
else:
    logging_file = os.path.join(os.getenv('HOME'),
                                'test.log')

print("Logging to", logging_file)

logging.basicConfig(
    level=logging.DEBUG,
    format='%(asctime)s : %(levelname)s : %(message)s',
    filename=logging_file,
    filemode='w',
)

logging.debug("Start of the program")
logging.info("Doing something")
logging.warning("Dying now")

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$ python stdlib_logging.py
Logging to /Users/swa/test.log

$ cat /Users/swa/test.log
2014-03-29 09:27:36,660 : DEBUG : Start of the program
2014-03-29 09:27:36,660 : INFO : Doing something
2014-03-29 09:27:36,660 : WARNING : Dying now

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>>> def get_error_details():
...     return (2, 'details')
...
>>> errnum, errstr = get_error_details()
>>> errnum
2
>>> errstr
'details'

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>>> a = 5; b = 8
>>> a, b
(5, 8)
>>> a, b = b, a
>>> a, b
(8, 5)

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>>> flag = True
>>> if flag: print('Yes')
...
Yes

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points = [{'x': 2, 'y': 3},
          {'x': 4, 'y': 1}]
points.sort(key=lambda i: i['y'])
print(points)

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$ python more_lambda.py
[{'y': 1, 'x': 4}, {'y': 3, 'x': 2}]

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listone = [2, 3, 4]
listtwo = [2*i for i in listone if i > 2]
print(listtwo)

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$ python more_list_comprehension.py
[6, 8]

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>>> def powersum(power, *args):
...     '''Return the sum of each argument raised to the specified power.'''
...     total = 0
...     for i in args:
...         total += pow(i, power)
...     return total
...
>>> powersum(2, 3, 4)
25
>>> powersum(2, 10)
100

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>>> mylist = ['item']
>>> assert len(mylist) >= 1
>>> mylist.pop()
'item'
>>> assert len(mylist) >= 1
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AssertionError

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from time import sleep
from functools import wraps
import logging
logging.basicConfig()
log = logging.getLogger("retry")


def retry(f):
    @wraps(f)
    def wrapped_f(*args, **kwargs):
        MAX_ATTEMPTS = 5
        for attempt in range(1, MAX_ATTEMPTS + 1):
            try:
                return f(*args, **kwargs)
            except:
                log.exception("Attempt %s/%s failed : %s",
                              attempt,
                              MAX_ATTEMPTS,
                              (args, kwargs))
                sleep(10 * attempt)
        log.critical("All %s attempts failed : %s",
                     MAX_ATTEMPTS,
                     (args, kwargs))
    return wrapped_f


counter = 0


@retry
def save_to_database(arg):
    print("Write to a database or make a network call or etc.")
    print("This will be automatically retried if exception is thrown.")
    global counter
    counter += 1
    # 这将在第一次调用时抛出异常
    # 在第二次运行时将正常工作（也就是重试）
    if counter < 2:
        raise ValueError(arg)


if __name__ == '__main__':
    save_to_database("Some bad value")

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$ python more_decorator.py
Write to a database or make a network call or etc.
This will be automatically retried if exception is thrown.
ERROR:retry:Attempt 1/5 failed : (('Some bad value',), {})
Traceback (most recent call last):
  File "more_decorator.py", line 14, in wrapped_f
    return f(*args, **kwargs)
  File "more_decorator.py", line 39, in save_to_database
    raise ValueError(arg)
ValueError: Some bad value
Write to a database or make a network call or etc.
This will be automatically retried if exception is thrown.