this post was submitted on 16 Mar 2026
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PEP: Is initializing typed variable with None bad practice? (lemmy.world)
submitted 19 hours ago by AstroLightz@lemmy.world to c/python@programming.dev
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For example:

class FooBar:
    def __init__(self):
        self.a: int = None
        self.foo: str = None

Is this bad practice/go against PEP guidelines or is it fine?

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[–] jtrek@startrek.website 6 points 19 hours ago (1 children)

That seems like that's going to give you an error in most type checkers. You said it's always an int and then immediate made that a lie and made it None instead.

Why are you trying to do this?

[–] AstroLightz@lemmy.world 2 points 18 hours ago (1 children)

I'm initializing variables that would be used later in the class in different functions. I wasn't sure if I needed to do a var: <type> | None = None or if just setting it to None was fine.

[–] solrize@lemmy.ml 2 points 11 hours ago* (last edited 11 hours ago) (1 children)

I'm going to say initializing them to None and updating them later is a code smell. If you can do so, make them non-optional and always initialize them to actual meaningful values.

[–] jtrek@startrek.website 2 points 7 hours ago

Yeah, if you initialize them to None then for the entire rest of the class you're going to have to account for the possibility that they're None. If it's unavoidable that they might be None, you should type it as such.

If you type them as like str | None then later when you do like return foo[0] it will warn you that you can't do that with None.