[issue44578] dict/list with more than two type parameters doesn't raise a TypeError

[Ken Jin]

Ken Jin <kenjin4096 at gmail.com> added the comment:

Sorry, I don't think this will be fixed as it is intentional. types.GenericAlias (the type of list[int] or dict[str, str]) does almost 0 checking for two reasons IIUC:

- Types with wrong number of parameters will usually be caught by your IDE/type checker.
- Checking would add complexity and slow down runtime performance. The current implementation of GenericAlias in C is intentionally simple.

We can add a note in the docs noting that too many type parameters won't raise a TypeError. It would probably be here https://docs.python.org/3/library/stdtypes.html#generic-alias-type

BTW, I adjusted the issue's affected versions because this was introduced only in 3.9.

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nosy: +gvanrossum, kj
versions: +Python 3.10, Python 3.11 -Python 3.7, Python 3.8

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