定义：在函数调用前后增加功能，但又不修改原函数的定义，这种在代码运行期间动态增加功能的方式，称之为“装饰器”

接受一个函数作为参数，并返回一个函数

模板如下：

def module(func):
    def wrapper(*args, **kw):
        print 'call deractor function.' 
        return func(*args, **kw)
    return wrapper

实例：提醒使用者使用的函数将废弃
decorator装饰之后的函数，它们的__name__已经从原来的test变成了deprecated， 返回的那个wrapper函数名字就是wrapper，所以，需要把原始函数的__name__等属性复制到test()函数中, 即_wrapped.func_name = func.func_name

def deprecated(func):

    def _wrapped(*args, **kwargs):
        print '*WARN* Keyword "%s" will deprecated' % func.__name__
        return func(*args, **kwargs)

    _wrapped.func_name = func.func_name

    return _wrapped

@deprecated
def test():
    print 'only for test'
    
test()
#result
*WARN* Keyword "test" will deprecated
only for test

其实相当于执行语句 deprecated（test）()

def test():
    print 'only for test'

deprecated(test)()
#result
*WARN* Keyword "test" will deprecated
only for test

接受一个传参作为参数，并返回一个函数

模板如下：

def module(arg):
    def decorator(func):
        def _wrapped(*args, **kwargs):
            print 'call deractor function, get a argument %s'  % arg
            return func(*args, **kw)
        return _wrapped
    return decorator

实例：提醒使用者使用的函数将废弃, 替换成其他函数

def deprecated(replacement):
    def deprecated(func):
        warning_msg = '*WARN* Keyword "%s" is deprecated, use "%s"' % (func.func_name, replacement)
        def _wrapped(*args, **kwargs):
            print(warning_msg)
            return func(*args, **kwargs)
        _wrapped.func_name = func.func_name
        return _wrapped
    return deprecated

@deprecated('for_test')
def test():
    print 'only for test'

test()
#result
*WARN* Keyword "test" is deprecated, use "for_test"
only for test

其实相当于执行语句 deprecated（'for_test'）(test)()

def test():
    print 'only for test'

deprecated('for_test')(test)()
#result
*WARN* Keyword "test" is deprecated, use "for_test"
only for test

常用总结

1.设置函数超时

import signal
import time

def set_timeout(timeout):
    def decorator(func):
        def handle(signum, frame):
            raise RuntimeError("Run function %s time out" % func.func_name)
        def wrapper(*args, **kwargs):
            signal.signal(signal.SIGALRM, handle)
            signal.alarm(timeout)
            result = func(*args, **kwargs)
            signal.alarm(0)
            return result
        wrapper.func_name = func.func_name
        return wrapper
    return decorator


@set_timeout(3)
def test():
    while True:
        time.sleep(1)
        print '111'

test()

#result
111
111
Traceback (most recent call last):
  File "/home/fantao/workspace/nbs/test.py", line 25, in <module>
    test()
  File "/home/fantao/workspace/nbs/test.py", line 11, in wrapper
    result = func(*args, **kwargs)
  File "/home/fantao/workspace/nbs/test.py", line 22, in test
    time.sleep(1)
  File "/home/fantao/workspace/nbs/test.py", line 7, in handle
    raise RuntimeError("Run function %s time out" % func.func_name)
RuntimeError: Run function test time out

2.设置函数运行多次

import functools

def run_times(times):
    def decorator(func):
        counter = {'times': 0}
        @functools.wraps(func)
        def wrapper(*args, **kw):
            for _ in range(times):
                func(*args, **kw)
        return wrapper
    return decorator

@run_times(3)
def test():
    print 'hello, world!'

test()
#result
hello, world!
hello, world!
hello, world!