CODEWITHSUNDEEP
pythonmypy
Jean-Francois T.
Jean-Francois T.

Reputation: 12950

Remove error from mypy for attributes set dynamically in a Python class

I am using mypy to check my Python code.

I have a class where I set dynamically some attributes and mypy keep on complaining about it:

error:"Toto" has no attribute "age"

This is my code:

class Toto:
    def __init__(self, name:str) -> None:
        self.name = name
        for attr in ['age', 'height']:
            setattr(self, attr, 0)


toto = Toto("Toto")
toto.age = 10  # "Toto" has no attribute "age" :(

Obviously, there could be 3 ways to solve the issue

  1. Ignoring the issue with # type: ignore: toto.age = 10 # type: ignore #...
  2. Using setattr to set the age of toto: setattr(toto, "age", 10)
  3. Setting the attributes explicitly (self.age = 0 ...)

However, I am looking for a more elegant and systematic way at the class level.

Any suggestion?

Upvotes: 14

Views: 5239

Answers (1)

jedwards
jedwards

Reputation: 30240

I don't follow mypy well enough to know whether this is (still, or ever was) the ideal work around, but this issue and this part of the cheatsheet indicate that something like:

from typing import Any

class Toto:
    def __init__(self, name:str) -> None:
        self.name = name
        for attr in ['age', 'height']:
            setattr(self, attr, 0)

    def __setattr__(self, name:str, value:Any):
        super().__setattr__(name, value)

toto = Toto("Toto")
toto.age = 10

Will allow you to do what you're doing without mypy complaining (which it does, just tested).

Any could be more restrictive, but the types will be checked on both setattr() and "traditional" obj.attr = ... calls, so heads up.

Upvotes: 7

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