There are a bunch of similar ones, see gh-12633. Unfortunately, there seems to be some issue/interaction with Python 3.5 (possibly a bug), which means that we could never merge those fixes. It seems that this one strikes the same issue. If you have any idea if/how to circumvent that, that would be awesome.

As an extra twist, the leak is only detected on Python 3.6 (and potentially other 3.X versions) and not on 2.X. We are using an older NumPy version internally but that part is unchanged from the current master.

Maybe the whole fix has to be applied only to >=3.6 due to the bug or just change in things. That is pretty annoying, but if we can figure out that it is only a few of the places where this is necessary, I suppose we could add some macros/compiler directives to fix it python version dependent...

Oh, so you found the work around that works on all python versions already? That is awesome, should we continue my old PR? I would could give you access to that branch.

I haven't tested locally on anything other than Python 3.5 and 3.6, but Azure covers 3.7 as well, right?

Feel free to include the PyObject_Free change in gh-12633. Your PR is much more comprehensive than this one.

I don't care too much either way. I already did that, but my PR is a bit larger (and thus review might be a bit slower). So after some thought I would also be happy to just merge this and rebase mine on top. I assume this is something you actually notice, so fixing it a bit faster may be good.
Can you remove the accidentally added old random files? (Or close if you prefer, if you are happy to review my changes, that would be much appreciated of course. There are a a couple of more I found, although there is also still a reference count leak I have not been able to find yet.)
The test coverage is a bit annoying, since I doubt everything gets covered, but since it is f2py, the coverage tools do not work out of the box...

@seberg Ping.

Ah, I forgot this over my gh-12633, but I can fix this up and merge it tomorrow or so.

Removed incorrect files, and changed it to tmp to apply my patch easier later. Will merge once tests pass, thanks!

Had to restart the PyPy test here (hanging process), just noting.