logging._handlerList is modified when setuptools Distribution is created #1139Description
Hi, CPython recently turned warnings into errors in its test suite via python/cpython#131802, and one of the unfortunate effects of that change is that when setuptools_scm is available on the system, on of the tests fails because logging._handlerList is modified during the execution.
The problem is that when setuptools_scm is available, creating setuptools Distribution adds a new hander to the list. It can be easily reproduced with this:
import logging
print(logging._handlerList)
from setuptools import Distribution
dist = Distribution()
print(logging._handlerList)which results in:
[<weakref at 0x7fc8fe73b970; to 'logging._StderrHandler' at 0x7fc8fef0e3c0>]
[<weakref at 0x7fc8fe73b970; to 'logging._StderrHandler' at 0x7fc8fef0e3c0>, <weakref at 0x7fc8fbadb8d0; to 'setuptools_scm._log.AlwaysStdErrHandler' at 0x7fc8f82bf4d0>]
which is unfortunate.
(It happens in Distribution.finalize_options where it loads all entry points in group "setuptools.finalize_distribution_options" - https://github.com/pypa/setuptools/blob/f37845bce6bb06ec25c24cf30210a485e945d21e/setuptools/dist.py#L786)
I reported the issue in the CPython issue tracker (python/cpython#133509 - more info is there) but after a discussion there I concluded that this is more of a setuptools_scm "issue" and I should ask here.
I am not sure whether this is a bug, but imho it's at least an unexpected side effect of just creating the Distribution instance. Should this be happening, and if so, is there a way of preventing this (or should be)? I believe this is the only setuptools plugin we have that is doing this.
Or (and I am aware this is more general question outside of setuptools_scm) would you maybe have a suggestion how to prevent the upstream Python test from failing? Thanks!