python decorators, nested function [duplicate]

I'm trying to figure out why i need a one more nested function when using decorators. Here is an example:

 def func(f):
    def deco(*args, **kwargs):
        return f(*args, **kwargs)
    return deco

@func
def sum(a, b):
    return a+b

print sum(5, 10)

Code works, everything is fine. But why do i need to create nested "deco" function? Let's try without it:

def func(f):
    return f(*args, **kwargs)

@func
def sum(a, b):
    return a+b

print sum(5, 10)

Code fails.

So there are three questions:

Why second sample does not works?
Why args,kwargs are "magically" appears if we are using a nested function?
What can i do, to make 2nd sample work? Except nesting another function, ofcourse.

Why second sample does not works?

Because you are calling the function on the return, you are not returning a function.
Why args,kwargs are "magically" appears if we are using a nested function?

They don't appear magically, we are declaring them, as in:
```
def deco(*args, **kwargs):
```
These are generic, and will match any function signature (argument list). You don't have to call them args and kwargs, that's just a convention, you could call them sharon and tracy.
What can i do, to make 2nd sample work? Except nesting another function, ofcourse.

Well you don't say what you expect the 2nd sample to do. But I guess to turn it into a decorator then:
```
def func(f):
    return f
```
But that's not doing a lot!

By the way, it is usually a bad idea to override an existing Python builtin (sum) - you have to have a very good reason for that.

来源：https://stackoverflow.com/questions/29474539/python-decorators-nested-function

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