Improve font weight guesser

Rufflewind · tacaswell · commit 0789e752da4a · 2017-06-27T22:14:38.000-04:00
diff --git a/lib/matplotlib/font_manager.py b/lib/matplotlib/font_manager.py
@@ -411,6 +411,7 @@ def ttfFontProperty(font):
     *font* is a :class:`FT2Font` instance.
     """
     name = font.family_name
+    style_name = font.style_name.lower().strip()
 
     #  Styles are: italic, oblique, and normal (default)
 
@@ -455,10 +456,14 @@ def ttfFontProperty(font):
                             reverse=True)
     weight = next((w for w in sorted_weights if sfnt4.find(w) >= 0), None)
     if not weight:
-        if font.style_flags & ft2font.BOLD:
-            weight = 700
-        else:
+        weight = next((w for w in weight_dict if style_name.find(w) >= 0), None)
+        if weight:
+            pass
+        elif style_name in ["italic", "oblique", "condensed"]:
             weight = 400
+        else:
+            # give up rather than risk making mistakes (reason: #8550)
+            raise KeyError("unknown weight: {!r}".format(font.family_name))
 
     #  Stretch can be absolute and relative
     #  Absolute stretches are: ultra-condensed, extra-condensed, condensed,
