How to use decorators to bring in functions and parameters?

Question

I have a piece of code as follows:

def range_print(n, *args):
    for i in range(n):
        func(i)
@range_print(n=10)
def func(i):
    print(i)

I get:

TypeError                                 Traceback (most recent call last)
<ipython-input-4-b13e44263521> in <module>
      2     for i in range(n):
      3         func(i)
----> 4 @range_print(n=10)
      5 def func(i):
      6     print(i)

<ipython-input-4-b13e44263521> in range_print(n, *args)
      1 def range_print(n, *args):
      2     for i in range(n):
----> 3         func(i)
      4 @range_print(n=10)
      5 def func(i):

TypeError: 'NoneType' object is not callable

Later I solved the problem, but I don't know if there is a better way? I want to use decorators to make my code look cleaner.

def range_print(n, *args):
    def inner(func): # <----Why do I need this def to load func？
        for i in range(n):
            func(i)
    return inner
@range_print(n=10)
def func(i):
    print(i)

Dewald Abrie · Accepted Answer · 2020-03-19 03:53:43Z

1

The reason why the function inner takes a function as a parameter, is that this is how the mechanics of Python work when you add a decorator like @range_print(n=10) to your function.

When you call your function, Python passes the function itself, together with its arguments, to the range_print decorator.

So in your case, the parameter named n in the range_print function signature is actually a function.

answered Mar 19, 2020 at 3:53

Dewald Abrie

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