How do I cleanly test equality of objects in Mypy without producing errors?

Question

I have the following function:

import pandas as pd

def eq(left: pd.Timestamp, right: pd.Timestamp) -> bool:
    return left == right

I get the following error when I run it through Mypy:

error: Returning Any from function declared to return "bool"

I believe this is because Mypy doesn't know about pd.Timestamp so treats it as Any. (Using the Mypy reveal_type function shows that Mypy treats left and right as Any.)

What is the correct way to deal with this to stop Mypy complaining?

Answer 1

you can cast it as a bool.

import pandas as pd

def eq(left: pd.Timestamp, right: pd.Timestamp) -> bool:
    return bool(left == right)

if mypy doesn't like that you can import cast from typing and use that to cast it to a bool.

import pandas as pd
from typing import cast

def eq(left: pd.Timestamp, right: pd.Timestamp) -> bool:
    result = bool(left == right)
    return cast(bool, result)

Answer 2

I have tested it also without using the cast command. The Mypy check is passed without any error with the following code:

import pandas as pd

def eq(left: pd.Timestamp, right: pd.Timestamp) -> bool:
    return bool(left == right)

(Tested with Mypy 0910.)