Perfect decorator in Python

@decorator can dynamically realize the increase of function function, however, after @decorator "transformation" function, compared with the original function, there is no other place than the function of a little more?

In the absence of decorator, print the function name:

def F1 (x):     Pass Print F1. __name__

Output:

F1

In the case of decorator, the function name is printed again:

def log (f):     def Wrapper (*args, * *kw)        :print'call... '        return F (*args, * *kw    )return  wrapper@logdef  F2 (x) :    passprint F2. __name__

Output:

Wrapper

As you can see, the new function functions returned by decorator are not ' F2 ', but are @log internally defined ' wrapper '. This will invalidate the code that relies on the name of the function. Decorator also changes other properties such as __doc__ of the function. If you want the caller to see that a function has undergone a @decorator transformation, you need to copy some of the properties of the original function into the new function:

def log (f):     def Wrapper (*args, * *kw)        :print'call... '        return F (*args, * *kw)    wrapper. __name__ = f.__name__    wrapper. __doc__ = f.__doc__    return Wrapper

It is inconvenient to write decorator because it is difficult to copy all the necessary properties of the original function to the new function, so Python's built-in Functools can be used to automate this "copy" task:

Import Functools def log (f):    @functools. Wraps (f)    def Wrapper (*args, * *kw)        :print  'call... '        return F (*args, * *kw    )return Wrapper

Finally, it is necessary to point out that since we have changed the original function signature (*args, **kw), we cannot get the original parameter information of the original function. Even if we use fixed parameters to decorate a function with only one parameter:

def log (f):    @functools. Wraps (f)    def  Wrapper (x):        print'  Call ... '        return f (x)     return Wrapper

It is also possible to change the parameter name of the original function because the parameter name of the new function is always ' x ', and the parameter name defined by the original function is not necessarily called ' X '.

Perfect decorator in Python