Warning: Expected type [Class Name], got 'Dict[str, int]' instead

Question

I'm building a class with methods that take dictionaries as inputs but Pycharm displays a warning.

''' Expected type 'TestClass', got 'Dict[str, int]' instead less... (⌘F1) Inspection info: This inspection detects type errors in function call expressions. Due to dynamic dispatch and duck typing, this is possible in a limited but useful number of cases. Types of function parameters can be specified in docstrings or in Python 3 function annotations '''

class TestClass:
    def __getitem__(self, index):
        return self[index]

    def get_keys(self):
        return list(self.keys())


dict_input = {'a':123, 'b':456}
TestClass.get_keys(dict_input)

So I get the warning here:

TestClass.get_keys(dict_input)

What does this warning mean and what's the approach to fix it?

Your code doesn't make much sense. get_keys is an instance method, you're supposed to call it on an instance of the class. But there is nowhere in your code that accepts a dict, so it's my clear where the keys are supposed to be coming from. — Daniel Roseman
get_key() is a method - it would normally be called on an instance of TestClass, NOT Testclass itself. It would take no parameters other than the implicit self passed to all methods, so I have no idea what that dict you're passing is supposed to do. — jasonharper

Jean Hominal Jean Hominal · Accepted Answer · 2019-10-12T20:54:49

A method such as the one you wrote is called an "instance method".

self, the receiver, should be an instance of TestClass (otherwise, many things could work wrong, such as super).

You could define get_keys as a static method, or use a simple function (without putting it in a class).

class TestClass:
    @staticmethod
    def get_keys(s):
        return list(s.keys())

You may want to read the Python documentation about classes for more details.

Warning: Expected type [Class Name], got 'Dict[str, int]' instead

2 Answers