Type checking

[sajith]

Running mypy --python-version 3.9 fabrictestbed_extensions/fablib/ reports hundreds of errors: "Found 488 errors in 12 files (checked 15 source files)", according to mypy 1.11.2, ran against commit 700964e.

Improving this situation should address issues like #295. We will need address the errors my reports, and run mypy on CI to prevent regressions.

Two things to note while adding static type checking:

• According to mypy docs (specifically using mypy with an existing codebase), adding mypy checks should be a gradual process, rather than one-shot.

• We have been mostly using Python 3.8 style type annotations. PEP 585 – Type Hinting Generics In Standard Collections has proposed some improvements, which are available since Python 3.9. So we'd be using list[str], dict[str, str] etc. rather than List[str], Dict[str,str], etc., which avoids the need for importing the typing module. See mypy type hints cheat sheet for some examples.