Compiling python 3.6.8 configured with --without-threads (no other options) fails, with undefined references to PyGILState_GetThisThreadState in pylifecycle.c, and PyGILState_Ensure and PyGILState_Release in object.c.

I used Louis' fix from issue #24784 in pylifecycle.c, and placed #ifdef WITH_THREADS around the undefined calls in object.c (both in _PyObject_dump). With this, compiling works.

Installing then fails because Lib/threading.py attempts to import _thread, which is not available. This can be fixed by replacing the import with the pattern described in _dummy_thread:

try:
    import _thread
except ImportError:
    import _dummy_thread as _thread

import _thread happens in two places in threading.py (the second is "from _thread import stack_size"); both have to be rewritten as above.

There is also an unguarded import _thread in telnetlib, but it's inside a method def (mt_interact in class Telnet) so perhaps it does not cause installation to fail.

Thanks for the report. Unfortunately, Python 3.6.8 was the last bugfix release of 3.6 so we now only accept and fix security-related issues for it.  I did a quick check and this does not appear to be a problem in 3.7.x but feel free to re-open the issue if it can be reproduced there.  Sorry!

https://devguide.python.org/#status-of-python-branches
https://devguide.python.org/devcycle/#security-branches

Not a problem. I wanted to record the issue just in case someone else encounters it, and also because there seems to have been a history of issues with the no-threads option. Happy to hear its sorted in 3.7.