TypeError: method() takes 3 arguments 4 were given

If you are beginner in python programming, it might be frustrating to see this type of error - TypeError: instance_method() takes 3 positional arguments but 4 were given.

You may wonder, you have given the right number of parameters as in the error, but how could it count one more.

TL;DR #

Python instance methods take first parameter as self (also known as this in other languages like java). So, in the error, if the required parameters are 3, first one will be self and others will be positional parameters that you need to pass.

So, if the error says takes n positional arguments but n+1 were given, method takes one self, and n-1 positional arguments. Pass n-1 positional arguments

Example #

This can be demonstrated with an example

class MyClass:
    def instance_method(self, p1, p2):
        print(f'parameters are: {p1}, {p2}')

def main():
    my_object = MyClass()
    my_object.instance_method('one', 'two', 'three')

main()

Output:

Traceback (most recent call last):
    ...
    ...
    my_object.instance_method('one', 'two', 'three')
TypeError: instance_method() takes 3 positional arguments but 4 were given

Here, my_object.instance_method('one', 'two', 'three') passed with 3 arguments as in the error and the error says, instance_method() takes 3 positional arguments but 4 were given.

But as we see, instance method takes only 2 parameters excluding self. Python internally passes self at runtime.

Here we just need to pass only two parameters while calling object method.