How do the arguments of a decorated function work?

user_16567651 0
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var = float(input('Enter a number: '))


def math_test(func):
    def wrapper(*args, **kwargs):
        func(var)
    return wrapper


@math_test
def times10(x):
    print(x * 10)


times10()

Why is it that when I call the function times10(), that I don't need to put the argument var in the brackets?

When I didn't type the argument var when I called func() I got an error saying requiring positional argument x...so when I put var in times10() I got the same error.

However when I placed the argument in func() it worked fine.

Shouldn't the wrapper function know that the argument in times10(), which would be var, should also be the argument in func()?

Edit:


var = float(input('Enter a number: '))


def math_test(func):
    def wrapper(*args, **kwargs):
        func(*args, **kwargs)
    return wrapper


@math_test
def times10(x):
    print(x * 10)

times10(var)
python-decorators python
1 Answers

This decorated function:

@math_test
def times10(x):
    print(x * 10)

Will be translated to:

times10 = math_test(times10)

Which means times10 is now equivalent to:

def wrapper(*args, **kwargs):
    func(var)

Where the callable func points to the original implementation of times10. To further visualize this, think of it as like this:

def times10(*args, **kwargs):
    def original_times10(x):
        print(x * 10)
    original_times10(var)
  • If you call func(var) which is synonymous above to original_times10(var) then it would work since original_times10 is passed var which would be put the argument x.
  • If you call func() which is synonymous above to original_times10(), it will obviously not work because original_times10 requires an input x but yet you didn't pass it anything.

Note that what you are trying to do is strictly passing a fixed argument var to the original implementation of times10:

func(var)

Depending on your usecase, I believe what you should be doing is passing the actual arguments:

func(*args, **kwargs)

This way, whatever you pass to the decorated function of times10 would be passed to the original implementation of times10.

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