Example:

import faulthandler
import time
import threading
threading.current_thread().name = "main_thread"
thr = threading.Thread(target=time.sleep, args=(2,), name="sleeper")
thr.start()
faulthandler.dump_traceback()
thr.join()

Output:

Thread 0x00007f58c25be6c0 [sleeper] (most recent call first):
  File "/home/vstinner/python/main/Lib/threading.py", line 996 in run
  File "/home/vstinner/python/main/Lib/threading.py", line 1054 in _bootstrap_inner
  File "/home/vstinner/python/main/Lib/threading.py", line 1016 in _bootstrap

Current thread 0x00007f58d06bb740 [main_thread] (most recent call first):
  File "/home/vstinner/python/main/x.py", line 7 in <module>

What about windows version? When I looked into it, I stopped on needing to move initialization from Modules/_threadmodule.c to Python/* and wasn't confident is it worth or no.

What about windows version?

I prefer to start only with Unix/BSD since the implementation is simpler. The Windows implementation can be added later.

cc @serhiy-storchaka

_PYTHREAD_NAME_MAXLEN may be undefined.

Oh right, I modified the code to require the macro in two code paths using it.

This would be a nice enhancement, but I think that it is better to use a buffer of size 100 than _PYTHREAD_NAME_MAXLEN.

Oh ok. I changed the buffer size to 100 bytes.

Merged, thanks for reviews.