QuLogic left a comment

Currently,    import weakref, matplotlib.ft2font    weakref.ref(matplotlib.ft2font.FT2Font("/usr/share/fonts/TTF/DejaVuSans.ttf"))aborts Py3 with    terminate called after throwing an instance of 'char const*'    Fatal Python error: Abortedwhereas on Py2 a normal `TypeError: cannot create weak reference to'matplotlib.ft2font.FT2Font' object` is raised.This is because the following happens:- Py3 sets the TypeError for failure to create a weakref.- The FT2Font object gets GC'd as nothing is referring to it (yes,  creating a weakref to a temporary is a bit silly).- The FT2Font destructor calls close_file_callback, which calls  mpl_PyFile_DupClose, which calls PyObject_AsFileDescriptor... which,  on Py3, calls the fileno() method on the file object.- PyObject_AsFileDescriptor fails because the originally set TypeError  has not been cleared, so mpl_PyFile_DupClose likewise fails, causing  close_file_callback to throw a C++ exception.Instead, carefully stash and restore the current exception state, bothin mpl_PyFile_DupClose, and likewise below, in mpl_PyFile_CloseFile (thelatter is needed because otherwise PyObject_CallMethod will clear theexception, cf comment in CPython's Objects/abstract.c:    /* PyObject_Call() must not be called with an exception set,    because it may clear it (directly or indirectly) and so the    caller loses its exception */Note that if an exception *actually* gets raised by mpl_PyFile_DupCloseor mpl_PyFile_CloseFile, it will overwrite the TypeError.  Strictlyspeaking, on Py3, it may be preferrable to chain the exceptions, butthis seems a bit overkill (mostly, I just want to avoid aborting thewhole Python process).