I have two functions, one which accepts lists or strings and returns the type that was input and another which accepts a string and calls the first function which is used in the result. A simplified example of this is: def accepts_string_or_list(inputs: str | list) -> str | list: if isinstance(inputs, list): return inputs + ['1'] return inputs + '1' def accepts_string(inputs: str) -> str: # do something to inputs string return accepts_string_or_list(inputs) Mypy complains on the very last line that "Incompatible return value type (got "str | list[Any]", expected "str") [return-value]mypy". I know that the accepts_string function will always accept a string which implies that the return value of accepts_string_or_list (when used in accepts_string) will always return a string. Mypy doesn't know this, but how do I make type hinting work correctly here? I know I could change the output type of accepts_string to be str | list instead of str. This would remove the error message, but would be untrue because only strings will be returned. For this reason, I would not want to do this. Continue reading...
