[Python] Trying to save mpl figure as pdf yields style flag error

I am trying to generate and save PDFs of Matplotlib figures using the Inter font.

I installed Inter with:

brew install font-inter


An example:

import matplotlib.pyplot as plt
import matplotlib.font_manager as fm

available_fonts = [f.name for f in fm.fontManager.ttflist]
if 'Inter' in available_fonts:
plt.rcParams['font.family'] = 'Inter'
else:
print("Inter font is not available. Please ensure it is installed.")

plt.rcParams['pdf.fonttype'] = 42 # for compatibility

# generate the figure
fig, ax = plt.subplots()
ax.plot([0, 1], [0, 1])
ax.set_title("Example Plot with Inter Font")
plt.show()

# save the figure
fig.savefig("example_plot.pdf", format='pdf')


I have no issues with this except on macOS, where I get the following error about the font's style flags:

$ /Users/atom/hemanpro/HeMan/.venv/bin/python /Users/atom/hemanpro/HeMan/misc_tools/addfont.py [13:58:58]
2025-01-02 13:59:29.100 Python[59655:1610342] +[IMKClient subclass]: chose IMKClient_Modern
2025-01-02 13:59:29.100 Python[59655:1610342] +[IMKInputSession subclass]: chose IMKInputSession_Modern
Traceback (most recent call last):
File "/Users/atom/hemanpro/HeMan/misc_tools/addfont.py", line 25, in <module>
fig.savefig("example_plot.pdf", format='pdf')
~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/Users/atom/hemanpro/HeMan/.venv/lib/python3.13/site-packages/matplotlib/figure.py", line 3490, in savefig
self.canvas.print_figure(fname, **kwargs)
~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^
File "/Users/atom/hemanpro/HeMan/.venv/lib/python3.13/site-packages/matplotlib/backend_bases.py", line 2184, in print_figure
result = print_method(
filename,
...<3 lines>...
bbox_inches_restore=_bbox_inches_restore,
**kwargs)
File "/Users/atom/hemanpro/HeMan/.venv/lib/python3.13/site-packages/matplotlib/backend_bases.py", line 2040, in <lambda>
print_method = functools.wraps(meth)(lambda *args, **kwargs: meth(
~~~~^
*args, **{k: v for k, v in kwargs.items() if k not in skip}))
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/Users/atom/hemanpro/HeMan/.venv/lib/python3.13/site-packages/matplotlib/backends/backend_pdf.py", line 2789, in print_pdf
file.finalize()
~~~~~~~~~~~~~^^
File "/Users/atom/hemanpro/HeMan/.venv/lib/python3.13/site-packages/matplotlib/backends/backend_pdf.py", line 827, in finalize
self.writeFonts()
~~~~~~~~~~~~~~~^^
File "/Users/atom/hemanpro/HeMan/.venv/lib/python3.13/site-packages/matplotlib/backends/backend_pdf.py", line 973, in writeFonts
fonts[Fx] = self.embedTTF(filename, chars)
~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^
File "/Users/atom/hemanpro/HeMan/.venv/lib/python3.13/site-packages/matplotlib/backends/backend_pdf.py", line 1416, in embedTTF
sf = font.style_flags
^^^^^^^^^^^^^^^^
File "/opt/homebrew/Cellar/python@3.13/3.13.1/Frameworks/Python.framework/Versions/3.13/lib/python3.13/enum.py", line 726, in __call__
return cls.__new__(cls, value)
~~~~~~~~~~~^^^^^^^^^^^^
File "/opt/homebrew/Cellar/python@3.13/3.13.1/Frameworks/Python.framework/Versions/3.13/lib/python3.13/enum.py", line 1207, in __new__
raise exc
File "/opt/homebrew/Cellar/python@3.13/3.13.1/Frameworks/Python.framework/Versions/3.13/lib/python3.13/enum.py", line 1184, in __new__
result = cls._missing_(value)
File "/opt/homebrew/Cellar/python@3.13/3.13.1/Frameworks/Python.framework/Versions/3.13/lib/python3.13/enum.py", line 1480, in _missing_
raise ValueError(
...<2 lines>...
))
ValueError: <flag 'StyleFlags'> invalid value 589824
given 0b0 10010000000000000000
allowed 0b0 00000000000000000011
.venvFAIL


To be clear, the figure is displaying the font correctly:



I've tried switching backends before saving the figure to Cairo, but that still gives the same error:

matplotlib.use("macosx") (at the top)
...
plt.show()
plt.switch_backend("Cairo")
fig.savefig("example_plot.pdf", format='pdf')


I've also tried QtAgg via PySide6.

Any ideas on what's going wrong and how to resolve it? Thanks!

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