Python中的闭包和装饰器
理解装饰器需要闭包的知识
https://segmentfault.com/a/1190000004461404
理解闭包：
This value in the enclosing scope is remembered even when the variable goes out of scope or the function itself is removed from the current namespace.
如何创建闭包（ref：https://www.programiz.com/python-programming/closure）：
The criteria that must be met to create closure in Python are summarized in the following points.
- We must have a nested function (function inside a function).
- The nested function must refer to a value defined in the enclosing function.
- The enclosing function must return the nested function.
使用闭包的好处和条件：
Closures can avoid the use of global values and provides some form of data hiding. It can also provide an object oriented solution to the problem.
When there are few methods (one method in most cases) to be implemented in a class, closures can provide an alternate and more elegant solutions. But when the number of attributes and methods get larger, better implement a class.
也就是说，当一个类中只有一个方法，那么用闭包来改写这个类更好。但是方法很多就不要用闭包了
关于装饰器：
从例子入手：
def deco_with_param(*args):
def inner(func):
print 'start with enclosing args', args
return func
return inner
def deco_without_param(func):
def inner(*args, **kw):
print 'start without enclosing ', args, kw
return func
return inner
def decos(*args):
def inner(func):
def inner1():
print 'inner1'
return func()
return inner1
return inner
print 'bar start'
@deco_without_param
def bar():
print 'In func bar'
print '-'*10
bar('bar value')
print 'bar end'
print
print 'may start'
@decos(123)
def may():
print 'In func may'
print '-'*10
may()
print 'may end'
print
print 'foo start'
@deco_with_param(123)
def foo():
print 'In func foo'
print '-'*10
foo()
print 'foo end'
#output
bar start
----------
start without enclosing ('bar value',) {}
bar end
may start
----------
inner1
In func may
may end
foo start
start with enclosing args (123,)
----------
In func foo
foo end
[Finished in 0.1s]
分析：
定义bar的时候：bar = deco_without_param(bar) = inner
调用bar的时候：bar() --> inner()
定义may的时候：may = decos(123)(may) = inner(may) = inner1
调用may的时候：may() --> inner1()
定义foo的时候：foo = deco_with_param(123)(foo) = inner(foo) [所以定义的时候就会输出] = func
另外，将 @functools.wraps(func)作为最内层函数的装饰器，可以保证被修饰的函数的__name__保持不变
