You should also add this:

    from __future__ import annotations

Then you will not get this error (NameError: name 'Sequence' is not defined) because it will not need the reference to `Sequence` for the annotation but the annotation is simply a string.

Using `if TYPE_CHECKING` is also useful when you want to speed up the module load time by not importing unnecessary modules (unnecessary at module load time).

And then, also to resolve import cycles, where you still want to annotate the function argument types.

One problem though: If this is a type/object which is not needed for module load time (there it's just used to annotate some function arg type), but which will be needed inside the function, type checkers and IDEs (e.g. PyCharm) will not show any problem, but then at runtime, you will the NameError once it tries to use the type/object.

Example module:

    from __future__ import annotations

    from typing import TYPE_CHECKING

    if TYPE_CHECKING:
        import torch

    def agi_model(query: torch.Tensor) -> torch.Tensor:
        torch.setup_secret_agi()
        ...

This module will load just fine, because `torch` is only needed for type checking at module load time. However, once you call this `agi_model` function, it will fail because `torch` is actually unknown at runtime. However, no IDE will show any problem with this code. (Edit: Eclipse/PyDev handles it correctly now, see answer below.)

Then you would add another `import torch` inside that `agi_model` function. However, then the IDE might even complain that this hides the outer scope `torch`.