[Python-Dev] Recent changes to PyCodeObject (original) (raw)

Steve Dower steve.dower at python.org
Wed Nov 16 19:44:46 EST 2016

On 16Nov2016 1618, Ned Batchelder wrote:

When I added Python 3.6 support to coverage.py, I posted a Mac wheel to PyPI: https://pypi.python.org/pypi/coverage/ That wheel was built against 3.6a3, the latest version at the time. When I use it now on 3.6b3, it doesn't work right. The reason is that the cofirstlineno field in PyCodeObject moved in September, as part of the PEP 523 work: https://github.com/python/cpython/commit/f1e6d88b3ca2b56d51d87b6b38ea1870c5d9490c

The docs say that PyCodeObject can change at any time, but I don't see why the field had to move in the first place. Was this needed?

IIRC, by reordering the fields we saved enough memory in padding that the new field did not take up any extra space (assuming 32-bit int and 64-bit pointers).

Am I doing the wrong thing by using PyCodeObject fields directly in the coverage.py C trace function? It seems like this was an unnecessary breaking change, even if it is a non-guaranteed interface.

I suspect the "wrong thing" here is expecting to not see any changes between alpha/beta versions. It certainly should not change within 3.6.x, so your wheel build will be fine, but changing during the prerelease versions is a possibility for anything not in the limited ABI.

Cheers, Steve

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