What backend are you using? I suspect the OSX backend from the error. Is that the full error message you get?

I can not reproduce this on py3 + linux + qtagg

attn @mdehoon

@tacaswell

Yes, it is the MacOSX backend, and the error message is all that I get.

If I manually specify the agg backend, it works normally as well. So this is a bug specific to OSX backend.

Which Matplotlib version do you use? I could not reproduce this on master (1.5.dev1)

@jenshnielsen

matplotlib (1.4.3)
Python 2.7.9
Mac OS X backend

I could not reproduce this with Python 2.7.9 and matplotlib 1.4.3 on Mac OS X 10.9 or 10.10.
Can you try changing backend_macosx.py to return immediately from _print_bitmap ?
So

        def _print_bitmap(self, filename, *args, **kwargs):
            return

Then, with some luck, we can find out exactly where the problem is occurring.

@mdehoon

The error message goes away, and obviously the jpg is never created.

I took the liberty of poking around in that function, and the error occurs in the call

self.write_bitmap(filename, width, height, dpi)

Even weirder is that running this script in ipdb line by line does not produce any error, and does produce a correct jpeg file.

I am guessing that these two lines:

    [image release];
    [resizedImage release];

in the function FigureCanvas_write_bitmap in _macosx.m are causing the problem. Can you try moving these two lines down to just before

    [pool release];

, recompile, and see if the problem still occurs?

@mdehoon

The problem still occurs after the change and recompile/reinstallation.

Deleting that two release calls doesn't help, either.

@mdehoon

I also tried recompiling python as well as installing matplotlib from this git repository. The assertion failure is still there.

Sorry, there is not much I can do as I cannot reproduce this error. I would suggest to remove more of the code in FigureCanvas_write_bitmap and see if the problem disappears at some point.

Possibly fixed by #6178, but since we're having trouble reproducing, it's hard to say.