An MWE:

Suppose a derived class NewDict from dict, and the setdefault is overriden.

I need to use the parent dict‘s method and keep some exception handlings from dict‘s method, like argument numbers handling.

So after some customized code, super().setdefault(key, default) is called.

class NewDict(dict):
    def setdefault(self, key, default):
        # some code checking key and default value
        return super().setdefault(key, default)

new_dict = NewDict()
new_dict.setdefault('key', 'value', 'wrong_argument')

But the error message shows unwanted number of arguments that counts additional self argument.

Traceback (most recent call last):
  File "/Users/test.py", line 7, in <module>
    new_dict.setdefault('key', 'value', 'wrong_argument')
TypeError: NewDict.setdefault() takes 3 positional arguments but 4 were given

Workaround

I know adding *args works, like:

class NewDict(dict):
    def setdefault(self, key, default, *args):
        # some code checking key and default value
        return super().setdefault(key, default, *args)

new_dict = NewDict()
new_dict.setdefault('key', 'value', 'wrong_argument')

then the message back to normal:

Traceback (most recent call last):
  File "/Users/test.py", line 7, in <module>
    new_dict.setdefault('key', 'value', 'wrong_argument')
  File "/Users/chzh/test.py", line 4, in setdefault
    return super().setdefault(key, default, *args)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: setdefault expected at most 2 arguments, got 3

but it seems silly just changing argument signature for such case.

Seek for

Is there any clean and elegant way to handle such problem?