python闭包

 1 def print_msg(msg):
 2 # This is the outer enclosing function
 3 
 4     def printer():
 5 # This is the nested function
 6         print(msg)
 7 
 8     printer()
 9 
10 # We execute the function
11 # Output: Hello
12 print_msg("Hello")

如上所示，printer是内嵌函数（nested function），根据LEGB的E原则，取到了传入的msg参数

def print_msg(msg):
# This is the outer enclosing function

    def printer():
# This is the nested function
        print(msg)

    return printer  # this got changed

# Now let‘s try calling this function.
# Output: Hello
another = print_msg("Hello")
another()

如果将print_msg内的printer调用替换成将其返回，赋值到变量another，print another会得到 ： <function printer at 0x02666AB0>， 可见赋值给another的是执行后的print_msg的值，即 printer，那么another()即代表执行printer()，而此时printer()仍然可以记得msg的值，即使print_msg函数已经结束执行，或者在another=print_msg("hello")后将print_msg删除，del print_msg也无妨。

闭包必须包含：

• We must have a nested function (function inside a function).　　     一个嵌套函数  
• The nested function must refer to a value defined in the enclosing function.      嵌套函数必须引用一个外部定义的变量
• The enclosing function must return the nested function.      enclosing函数返回嵌套函数

__closure__

closure属性返回一个包含cell的元组，里面每个cell保存了作用域变量

print another.__closure__

>>> (<cell at 0x024FC990: str object at 0x024FC960>,)

print another.__closure__[0].cell_contents

>>>Hello

参考：https://www.programiz.com/python-programming/closure

python闭包

原文：http://www.cnblogs.com/tachikoma-/p/7582739.html