Rely on findfont autofallback-to-default in pdf/ps backends.

findfont(...) will never return None unless fallback_to_default=False
is passed -- the default is True and causes afm searches to fall
back to Helvetica -- so the "filename is None" branch never occurs.
(The code in the pdf/ps backends came in in af9954d (2009) whereas
fallback_to_default only came in in 94120dc (2010).)

Author: anntzer

lib/matplotlib/backends/_backend_pdf_ps.py

@@ -69,11 +69,8 @@ def get_text_width_height_descent(self, s, prop, ismath):
             return w, h, d
 
     def _get_font_afm(self, prop):
-        fname = (
-            font_manager.findfont(
-                prop, fontext="afm", directory=self._afm_font_dir)
-            or font_manager.findfont(
-                "Helvetica", fontext="afm", directory=self._afm_font_dir))
+        fname = font_manager.findfont(
+            prop, fontext="afm", directory=self._afm_font_dir)
         return _cached_get_afm_from_fname(fname)
 
     def _get_font_ttf(self, prop):

lib/matplotlib/backends/backend_pdf.py

@@ -663,10 +663,6 @@ def fontName(self, fontprop):
         elif rcParams['pdf.use14corefonts']:
             filename = findfont(
                 fontprop, fontext='afm', directory=RendererPdf._afm_font_dir)
-            if filename is None:
-                filename = findfont(
-                    "Helvetica",
-                    fontext='afm', directory=RendererPdf._afm_font_dir)
         else:
             filename = findfont(fontprop)