GeezerVison

inspect.getframeinfo() and traceback read the current instruction with
itertools.islice(code.co_positions(), lasti // 2). co_positions() yields
one tuple per instruction, so islice builds and discards a tuple for
every preceding instruction. Callers such as inspect.stack(0) do this
for every frame, and the cost grows with the size of the code object.

The byte offset is the same value traceback.c already passes to
PyCode_Addr2Location. Expose that lookup as the private method
code._co_position_at() and use it for real code objects. The returned
tuple matches co_positions(), including None where a column is missing.
Objects that only implement co_positions() keep the iterator path.
Filename selection is unchanged.

Co-authored-by: Cursor <[email protected]>

blurb rejects gh-issue-0, which failed the documentation build.

Co-authored-by: Cursor <[email protected]>