matplotlib · colt-1 · Nov 6, 2019 · Nov 6, 2019 · Nov 6, 2019 · Nov 6, 2019
diff --git a/doc/api/next_api_changes/behaviour.rst b/doc/api/next_api_changes/behaviour.rst
@@ -36,3 +36,8 @@ did nothing, when passed an unsupported value. It now raises a ``ValueError``.
 `.Axis.set_tick_params` (and the higher level `.axes.Axes.tick_params` and
 `.pyplot.tick_params`) used to accept any value for ``which`` and silently
 did nothing, when passed an unsupported value. It now raises a ``ValueError``.
+
+``font_manager.findfont`` now warns of +-100 weight difference of selected font vs found font
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Fonts are mapped from string to number. If the best-matched font is over 100 less than or
+greater than the chosen font, a warning will be logged.
diff --git a/lib/matplotlib/font_manager.py b/lib/matplotlib/font_manager.py
@@ -86,6 +86,10 @@
     'extra bold': 800,
     'black':      900,
 }
+
+def map_weight_name_to_score(weight):
+    return weight if isinstance(weight, Number) else weight_dict[weight]
+
 font_family_aliases = {
     'serif',
     'sans-serif',
@@ -1147,8 +1151,8 @@ def score_weight(self, weight1, weight2):
         # exact match of the weight names, e.g. weight1 == weight2 == "regular"
         if cbook._str_equal(weight1, weight2):
             return 0.0
-        w1 = weight1 if isinstance(weight1, Number) else weight_dict[weight1]
-        w2 = weight2 if isinstance(weight2, Number) else weight_dict[weight2]
+        w1 = map_weight_name_to_score(weight1)
+        w2 = map_weight_name_to_score(weight2)
         return 0.95 * (abs(w1 - w2) / 1000) + 0.05
 
     def score_size(self, size1, size2):
@@ -1275,6 +1279,11 @@ def _findfont_cached(self, prop, fontext, directory, fallback_to_default,
                 best_font = font
             if score == 0:
                 break
+        if best_font is not None:
+            if abs(map_weight_name_to_score(prop.get_weight())
+                - map_weight_name_to_score(best_font.weight)) > 100:
+                _log.warning('findfont: Failed to find font weight %s, '
+                + 'now using %s.', prop.get_weight(), best_font.weight)
 
         if best_font is None or best_score >= 10.0:
             if fallback_to_default:

diff --git a/lib/matplotlib/tests/test_font_manager.py b/lib/matplotlib/tests/test_font_manager.py
@@ -13,7 +13,7 @@
 from matplotlib.font_manager import (
     findfont, findSystemFonts, FontProperties, fontManager, json_dump,
     json_load, get_font, get_fontconfig_fonts, is_opentype_cff_font,
-    MSUserFontDirectories, _call_fc_list)
+    MSUserFontDirectories, _call_fc_list, map_weight_name_to_score, weight_dict)
 from matplotlib import pyplot as plt, rc_context
 
 has_fclist = shutil.which('fc-list') is not None
@@ -199,3 +199,25 @@ def test_fork():
     _model_handler(0)  # Make sure the font cache is filled.
     ctx = multiprocessing.get_context("fork")
     ctx.Pool(processes=2).map(_model_handler, range(2))
+
+def test_map_weights():
+    assert map_weight_name_to_score('ultralight') == 100
+    assert map_weight_name_to_score('light') == 200
+    assert map_weight_name_to_score('normal') == 400
+    assert map_weight_name_to_score('regular') == 400
+    assert map_weight_name_to_score('book') == 400
+    assert map_weight_name_to_score('medium') == 500
+    assert map_weight_name_to_score('roman') == 500
+    assert map_weight_name_to_score('semibold') == 600
+    assert map_weight_name_to_score('demibold') == 600
+    assert map_weight_name_to_score('demi') == 600
+    assert map_weight_name_to_score('bold') == 700
+    assert map_weight_name_to_score('heavy') == 800
+    assert map_weight_name_to_score('extra bold') == 800
+    assert map_weight_name_to_score('black') == 900
+
+def test_font_match_warning():
+        with warnings.catch_warnings(record=True) as warns:
+            font = findfont(FontProperties(family=["PingFang SC"], weight=900))
+            assert len(warns) == 2
+