Bug report

Checklist

• I am confident this is a bug in CPython, not a bug in a third-party project
• I have searched the CPython issue tracker, and am confident this bug has not been reported before

A clear and concise description of the bug

Doctests initialization may fail with re.error in case a module contains (dynamically generated) class objects with special characters in their name. This is caused by the regular expression compiled in doctest.DocTestFinder._find_lineno failing to escape the class name before embedding it. If compilation does succeed, then invalid matches may result from interpreting the class name as a search pattern.

Your environment

• CPython versions tested on: 3.9.2
• Operating system and architecture: Debian linux amd64

Linked PRs

• gh-107715: Escape class name in regular expression #107716
• [3.12] gh-107715: Escape class name in regular expression (GH-107716) #107726
• [3.11] gh-107715: Escape class name in regular expression (GH-107716) #107727