Fix typing of external APIs

[jemrobinson]

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⤴️ Summary

Fix typing issues arising from external Azure SDK libraries

🌂 Related issues

n/a

🔬 Tests

Tested locally

[JimMadge]

I remember talking about this. Did typing.cast turn out to be the most sensible thing to do (or at least more sensible than ignoring types)?

[jemrobinson]

Possible options (ordered by how much I like them)

1. Get Microsoft to fix their type hints
2. Write our own type hints (turns out to be too much work in this case)
3. Use cast to manually specify the type we know is returned
4. Ignore type hints

If you'd like to try (1) or (2) then feel free :)

[JimMadge]

Agreed that an upstream fix is probably the real answer.

I wouldn't want to maintain our own type hints for large, third-party libraries just to make mypy pass though. I think casts or ignores are better in that case.

Maybe a rule of thumbs is,

• typing.cast when you are very confident about the static type
• ignore when the type is not static or is poorly defined