Bug report

As originally reported in http://gnats.netbsd.org/53425 , with matplotlib version 2.2.2, attempting to import matplotlib.pyplot on a NetBSD system fails with:

Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/usr/pkg/lib/python2.7/site-packages/matplotlib/pyplot.py", line 31, in <module>
    import matplotlib.colorbar
  File "/usr/pkg/lib/python2.7/site-packages/matplotlib/colorbar.py", line 36, in <module>
    import matplotlib.contour as contour
  File "/usr/pkg/lib/python2.7/site-packages/matplotlib/contour.py", line 20, in <module>
    import matplotlib.font_manager as font_manager
  File "/usr/pkg/lib/python2.7/site-packages/matplotlib/font_manager.py", line 1469, in <module>
    _rebuild()
  File "/usr/pkg/lib/python2.7/site-packages/matplotlib/font_manager.py", line 1450, in _rebuild
    fontManager = FontManager()
  File "/usr/pkg/lib/python2.7/site-packages/matplotlib/font_manager.py", line 1086, in __init__
    self.ttflist = createFontList(self.ttffiles)
  File "/usr/pkg/lib/python2.7/site-packages/matplotlib/font_manager.py", line 587, in createFontList
    font = ft2font.FT2Font(fpath)
TypeError: First argument must be a path or file object reading bytes

I tracked down the cause of this to mpl_PyFile_Dup() attempting to call the "flush" method of a file object that is open only for reading. Python implements this by calling fflush(), and calling fflush() on a file descriptor not open for writing is treated as an error on BSD systems (but silently ignored on Linux). The fflush() call returns -1 with errno=EBADF, and this ultimately gets translated into the rather unhelpful error message "TypeError: First argument must be a path or file object reading bytes" show above.

The call chain leading to the error is PyFT2Font_init() -> convert_open_args() -> mpl_PyFile_Dup().

Code for reproduction

On a BSD system, run

python2.7 -c 'import matplotlib.pyplot'

Actual outcome

The stack trace shown above is printed.

Expected outcome

The command silently exits with a success status.

Matplotlib version

• Operating system: NetBSD 7.1_STABLE
• Matplotlib version: 2.2.2
• Matplotlib backend (print(matplotlib.get_backend())): GTKAgg
• Python version: 2.7.15
• Jupyter version (if applicable): N/A
• Other libraries: N/A

matplotlib was installed via pkgsrc.

I have a patch which I will attempt to submit as a pull request.