this post was submitted on 06 Jul 2023
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When to use typing.TYPE_CHECKING (feddit.de)
submitted 1 year ago* (last edited 1 year ago) by [email protected] to c/[email protected]
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After learning about TYPE_CHECKING i made it a habit to put all imports that were only needed for type checking into an if TYPE_CHECKING: guard. But now I am wondering if that is actually intended to be used like that. Checking whether an import is only needed at type checking time can get quite tedious and sometimes you run into situations were you introduced some code that made the import a requirement at runtime.

How do you use TYPE_CHECKING? Whenever it is possible or only when using it actually solves a circular import?

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[–] [email protected] 1 points 1 year ago (1 children)

You still need to import the type before using it in a stringified type annotation for it to be valid though, so you'd need the import in an if TYPE_CHECKING: block either way, no?

[–] [email protected] 2 points 1 year ago (1 children)

Yes, but if it’s in a TYPE_CHECKING block I can ONLY use the annotation with quotes*, which is why I only use that method if I must.

  • except with from __future__ import annotations as I’ve just learned.
[–] [email protected] 1 points 1 year ago

Ah yeah, I see what you meant.