Disable the compilation of the built-in _abc module. For example, on Python 3.7 apply the following patch: diff --git a/Modules/Setup.dist b/Modules/Setup.dist index 8cc6bf0540..4015527b32 100644 --- a/Modules/Setup.dist +++ b/Modules/Setup.dist @@ -114,7 +114,7 @@ _weakref _weakref.c # weak references _functools -DPy_BUILD_CORE _functoolsmodule.c # Tools for working with functions and callable objects _operator _operator.c # operator.add() and similar goodies _collections _collectionsmodule.c # Container types -_abc _abc.c # Abstract base classes +#_abc _abc.c # Abstract base classes itertools itertoolsmodule.c # Functions creating iterators for efficient looping atexit atexitmodule.c # Register functions to be run at interpreter-shutdown _signal -DPy_BUILD_CORE signalmodule.c @@ -363,7 +363,8 @@ xxsubtype xxsubtype.c # Uncommenting the following line tells makesetup that all following modules # are not built (see above for more detail). # -#*disabled* +*disabled* # #_sqlite3 _tkinter _curses pyexpat #_codecs_jp _codecs_kr _codecs_tw unicodedata +_abc Recompile Python, check: $ ./python -c 'import _abc' ModuleNotFoundError: No module named '_abc' Run: $ ./python -u -m test -R 3:3 test_functools -m test_mro_conflicts Error without _abc: test test_functools crashed -- Traceback (most recent call last): File "/home/vstinner/prog/python/3.7/Lib/test/libregrtest/runtest.py", line 180, in runtest_inner refleak = dash_R(the_module, test, test_runner, ns.huntrleaks) File "/home/vstinner/prog/python/3.7/Lib/test/libregrtest/refleak.py", line 71, in dash_R abcs) File "/home/vstinner/prog/python/3.7/Lib/test/libregrtest/refleak.py", line 148, in dash_R_cleanup obj.register(ref()) File "/home/vstinner/prog/python/3.7/Lib/_py_abc.py", line 60, in register raise TypeError("Can only register classes") TypeError: Can only register classes With built-in _abc module, regrtest is fine. The problem comes from pure-Python reimplementation of abc._get_dump() in Lib/test/libregrtest/refleak.py: def _get_dump(cls): # For legacy Python version return (cls._abc_registry, cls._abc_cache, cls._abc_negative_cache, cls._abc_negative_cache_version) The first item tuple must be a set of weak references. Currently, it's a weak set of strong references. Attached PR fix the issue.

 New changeset 79b5d29041bd85ea3baa050b3fa2481344ea35c9 by Victor Stinner in branch 'master': bpo-36565: Fix libregrtest for Python without builtin _abc (GH-12733) https://github.com/python/cpython/commit/79b5d29041bd85ea3baa050b3fa2481344ea35c9 

 New changeset 2368d86ed1249505b10561e005fc57f4884619c1 by Victor Stinner (Miss Islington (bot)) in branch '3.7': bpo-36565: Fix libregrtest for Python without builtin _abc (GH-12733) (GH-12734) https://github.com/python/cpython/commit/2368d86ed1249505b10561e005fc57f4884619c1