Following our discussion on the previous PR, I also changed the _cursesmodule prefix to cursesmodule so that we have at least a bit more of consistency. I won't touch the AC-generated functions.

I'm really un-sure of how free-threaded builds with multi-phase initialization would interact with capsule objects. So I'd happy if any free-threaded expert could help me here. Here are some questions (and we may perhaps address them in separate PRs):

• Should the global flags (simple int) be atomically set?
• Should we use PyRawMem_* instead of PyMem_* functions when allocating the memory for capsule objects?
• Why am I only seeing the assertion failure on my pointer not NULL when I converted it into a multi-phase initialization module and not before? (see 9e0dd70 for the commit who actually "fixed" it).

cc @colesbury (I don't know other free-threaded experts but feel free to delegate the question to anyone who knows about the topic if you don't have enough time!)

Here's the output, do you think it's good enough?

>>> import sys
...
>>> import _curses as curses1
>>> del sys.modules['_curses']
...
>>> import _curses as curses2
...
Traceback (most recent call last):
  File "<python-input-3>", line 1, in <module>
    import _curses as curses2
ImportError: module 'curses' can only be loaded once per process

cursesmodule_free() should set curses_module_loaded to 0. So you can load-unload the extension multiple times:

import sys
import gc

print("load-unload")
import _curses
del _curses
del sys.modules['_curses']
gc.collect()

print("load again")
import _curses
del _curses
del sys.modules['_curses']

cursesmodule_free() should set curses_module_loaded to 0. So you can load-unload the extension multiple times:

I'm not sure it works. Even if I do this it still tells me that the curses module cannot be loaded more than once per process. The cursesmodule_free() does not seem to be called even if gc.collect() is called (at least not in the REPL). What should I do?

The cursesmodule_free() does not seem to be called even if gc.collect() is called (at least not in the REPL).

It works if you run my script:

load-unload
load again

After some tests, it appears that the REPL only calls free() upon exiting the process (the REPL imports curses in Lib/_pyrepl/curses.py). So, reloading curses inside the REPL won't work. In a normal script, however:

$ read -r -d '' code << EOM
import sys

print("load-unload")
import _curses
del _curses
del sys.modules['_curses']

print("load again")
import _curses
del _curses
del sys.modules['_curses']
EOM
$ ./python -c "$code"
load-unload
load again
Traceback (most recent call last):
  File "<string>", line 9, in <module>
    import _curses
ImportError: module 'curses' can only be loaded once per process

When free is called via gc.collect():

$ read -r -d '' code << EOM
import sys
import gc

print("load-unload")
import _curses
del _curses
del sys.modules['_curses']
gc.collect()

print("load again")
import _curses
del _curses
del sys.modules['_curses']
EOM
$ ./python -c "$code"
load-unload
load again

Merged, thanks. That's a nice step forward for the _curses extension :-)

Python no longer leaks at exit:

$ ./python -X showrefcount -c 'import _curses'
[0 refs, 0 blocks]

Python 3.13 for comparison:

$ ./python -X showrefcount -c 'import _curses'
[234 refs, 159 blocks]