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I eventually also found out that the `typing` module has a global variable [`TYPE_CHECKING`](https://docs.python.org/3/library/typing.html#typing.TYPE_CHECKING) that can be used to only import during type-checking.
Concretely, the following code for `helpers.py` seems to type-check fine as well.
```python
from typing import TYPE_CHECKING

if TYPE_CHECKING:
    from process import Process

class Helper:
    
    def update(self, process: "Process"):
        ...
```

The [other answer](https://software.codidact.com/posts/289455/289481#answer-289481) probably is the better way to go in the context of circular imports, since this functionality is mainly intended for costly imports (according to the docs).