Improve traceback.FrameSummary

[AlexWaygood]

• Add missing __len__ method.
• linenocan be None
• line is a read-only property that can be stror None, not a str attribute.
• Improve __getitem__ with overloads.
• Reflect changes to the class that have been made in 3.11 (new __init__ signature, new instance attributes).

Source code here: https://github.com/python/cpython/blob/b27195332e91e932501f16cf9877761b218a9c99/Lib/traceback.py#L243

[AlexWaygood]

Diff from mypy_primer, showing the effect of this PR on open source code:

core (https://github.com/home-assistant/core) + homeassistant/util/async_.py:158: error: Item "None" of "Optional[str]" has no attribute "strip" [union-attr]+ homeassistant/util/async_.py:164: error: Item "None" of "Optional[str]" has no attribute "strip" [union-attr]+ homeassistant/helpers/frame.py:112: error: Item "None" of "Optional[str]" has no attribute "strip" [union-attr]

Arguably these are true positives: linecan clearly be None

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

werkzeug (https://github.com/pallets/werkzeug) + src/werkzeug/debug/tbtools.py:378: error: Unsupported operand types for - ("None" and "int") [operator]+ src/werkzeug/debug/tbtools.py:378: note: Left operand is of type "Optional[int]" pyp (https://github.com/hauntsaninja/pyp) + pyp.py:641: error: Argument 1 to "code_for_line" has incompatible type "Optional[int]"; expected "int" core (https://github.com/home-assistant/core) + homeassistant/util/async_.py:158: error: Item "None" of "Optional[str]" has no attribute "strip" [union-attr]+ homeassistant/util/async_.py:164: error: Item "None" of "Optional[str]" has no attribute "strip" [union-attr]+ homeassistant/helpers/frame.py:112: error: Item "None" of "Optional[str]" has no attribute "strip" [union-attr]

[hauntsaninja]

@AlexWaygood any idea under what circumstances lineno can be None?

edit: I got misled by something, removed some noise

[hauntsaninja]

In practice it looks like lineno's in traceback come from https://github.com/python/cpython/blob/b27195332e91e932501f16cf9877761b218a9c99/Lib/traceback.py#L329

which we have as an int

typeshed/stdlib/types.pyi

Line 520 in e3d4bdc

deftb_lineno(self) ->int: ...

[AlexWaygood]

https://github.com/python/cpython/blob/b27195332e91e932501f16cf9877761b218a9c99/Lib/traceback.py#L305looks pretty reachable to me, but I'll confess I don't know what real-life code ends up with us getting there :)

[hauntsaninja]

So should we be changing TracebackType.tb_lineno?

[AlexWaygood]

I don't know. I'm not an exception-handling expert, and the language reference doesn't shed much light here. Feel free to revert the int -> int | None changes if you're confident I'm incorrect here :)

[Akuli]

This might have something to do with #6769. Presumably traceback line numbers come from stack frames.