CODEWITHSUNDEEP
pythonargumentsdecoratorpython-decorators
László Marton
László Marton

Reputation: 87

Modify *args by decorator in python

I would like to check and change, if necessary, the type of a function's parameter with decorator, i.e. something like that:

def convert_argument_types(func):
    def inner(*args):
        for arg in args:
            if not isinstance(arg, something):
                arg = convertToSomething(arg)
        return func(*args)

    return inner

@convert_argument_types # I would like to apply it to functions with unknown number of parameters
def someFunction(arg1, arg2):
    pass

I tried of course within the inner function the following:

return func(args)

But it doesn't work, doesn't change the type of *args.

Of course, by knowing the number of parameters, I could do for each number of parameters smg like:

def convert_two_argument_types(func):
   def inner(arg, arg2):
       if not isinstance(arg, something):
           arg = convertToSomething(arg)
    
       if not isinstance(arg2, something):
           arg2 = convertToSomething(arg2)

       return func(arg, arg2)
   return inner

with convert_one/two/three/etc_argument_types(), but it is everything, but not elegant.

Is there a way to solve my issue by using decorators? What would be the most elegant way?

Thank you for your help!

Upvotes: 0

Views: 1239

Answers (1)

Barmar
Barmar

Reputation: 781059

Assigning to arg has no effect on args; the variable gets a reference to the value of the tuple element, not a reference to the tuple itself.

In addition, since tuples are immutable, you can't modify it in place.

Use a list comprehension to make a new list with the modified values.

args = [arg if isinstance(arg, something) else convertToSomething(arg) for arg in args]

Upvotes: 1

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