Use repr in scatter error message (#24403)

jefromyers · web-flow · commit 04ce3e990234 · 2022-11-10T18:30:15.000-05:00
* use repr in error message closes #21959 * add test for repr error message * fix formatting * clean up formatting and naming * add `pragma: no cover` * remove import and function name a bit more explicit
diff --git a/lib/matplotlib/axes/_axes.py b/lib/matplotlib/axes/_axes.py
@@ -4416,7 +4416,7 @@ def invalid_shape_exception(csize, xsize):
                     # severe failure => one may appreciate a verbose feedback.
                     raise ValueError(
                         f"'c' argument must be a color, a sequence of colors, "
-                        f"or a sequence of numbers, not {c}") from err
+                        f"or a sequence of numbers, not {c!r}") from err
             else:
                 if len(colors) not in (0, 1, xsize):
                     # NB: remember that a single color is also acceptable.
diff --git a/lib/matplotlib/tests/test_axes.py b/lib/matplotlib/tests/test_axes.py
@@ -8290,3 +8290,17 @@ def test_extent_units():
     with pytest.raises(ValueError,
                        match="set_extent did not consume all of the kwargs"):
         im.set_extent([2, 12, date_first, date_last], clip=False)
+
+
+def test_scatter_color_repr_error():
+
+    def get_next_color():
+        return 'blue'  # pragma: no cover
+    msg = (
+            r"'c' argument must be a color, a sequence of colors"
+            r", or a sequence of numbers, not 'red\\n'"
+        )
+    with pytest.raises(ValueError, match=msg):
+        c = 'red\n'
+        mpl.axes.Axes._parse_scatter_color_args(
+            c, None, kwargs={}, xsize=2, get_next_color_func=get_next_color)
