Python的装饰器

>>> def now():
...     print '2013-12-25'

def log(text):
    def decorator(func):
        def wrapper(*args, **kw):
            print '%s %s():' % (text, func.__name__)
            return func(*args, **kw)
        return wrapper
    return decorator

定义了装饰器log

@log('execute')
def now():
    print '2013-12-25'

运行结果：

>>> now()
execute now():
2013-12-25

3层嵌套的效果是这样的：

>>> now = log('execute')(now)

自己思考的时候想过能不能将代码改为如下：

>>> def log(text):
...     def decorator(func):
...         def wrapper(*args, **kw):
...             print '%s %s():' % (text, func.__name__)
...             return func(*args, **kw)
...         #return wrapper
...     return decorator
... 
>>> @log('hello')
... def now():
...     print '2013-12-25'

结果：

>>> now()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'NoneType' object is not callable
>>> 

因为嵌套效果为：

>>> now = log('execute')(now)

但由于｀decorator函数没有返回函数，所以now`不能在执行调用