This piece of code is what I'm using to clarify certain function-related concepts in Python, especially those relating to decorators

test_deco.py

# Test decorator functionality in Python
def log(F):
    def print_args(*args, **kwargs):
        print args, kwargs
    return print_args
  
@log
def holy_smokes(a, b, c):
    print a + b + c
  
if __name__ == "__main__":
    holy_smokes(1,2,3)

Now, according to PEP-318, this leads to the function transformation

@log
def holy_smokes():
    pass

to

def holy_smokes():
    pass
holy_smokes = log(holy_smokes)

What took me a long time to understand was that this was a function transformation. My confusion can be clarified by comparing it to what its not:

holy_smokes = log(holy_smokes(1,2,3))

In this case, the return value is passed to log, whereas in the previous case the function itself was passed.

Question: how are the args of holy_smokes being printed, when there is no clear relation between that and print_args? I cannot see how this works, using my standard view of functions: clearly, log is given an input argument holy_smokes, so we should substitute holy_smokes instead of F in the function definition. And what is
returned? A different function! This new function does only one thing: prints out values of its input arguments. It has no relation to the input function F!

So there's nothing mysterious going on here. You're just making the same mistake repeatedly of not being able to distinguish between function definition and function call!

Nice Resources on Decorators:
http://www.siafoo.net/article/68
http://simeonfranklin.com/blog/2012/jul/1/python-decorators-in-12-steps/