matplotlib · ramaini · Mar 31, 2023 · Mar 31, 2023 · Mar 31, 2023 · Mar 31, 2023
diff --git a/doc/users/next_whats_new/updated_scatter.rst b/doc/users/next_whats_new/updated_scatter.rst
@@ -0,0 +1,19 @@
+Enable configuration of empty markers in `~matplotlib.axes.Axes.scatter`
+------------------------------------------------------------------------
+
+`~matplotlib.axes.Axes.scatter` can now be configured to plot empty markers 
+without additional code. Setting ``facecolors`` to *'none'* and
+defining ``c`` now draws only the edge colors for fillable markers. This
+allows empty face colors and non-empty edge colors without disrupting
+existing color-mapping capabilities.
+
+.. plot::
+    :include-source: true
+    :alt: A simple scatter plot which illustrates the use of the *scatter* function to plot empty markers.
+
+    import numpy as np
+    import matplotlib.pyplot as plt
+
+    x = np.arange(0, 10)
+    plt.scatter(x, x, c=x, facecolors='none', marker='o')
+    plt.show()
diff --git a/lib/matplotlib/axes/_axes.py b/lib/matplotlib/axes/_axes.py
@@ -4313,6 +4313,8 @@ def _parse_scatter_color_args(c, edgecolors, kwargs, xsize,
 
         Argument precedence for facecolors:
 
+        - kwargs['facecolor'] if 'none'
+        - kwargs['facecolors'] if 'none'
         - c (if not None)
         - kwargs['facecolor']
         - kwargs['facecolors']
@@ -4324,6 +4326,7 @@ def _parse_scatter_color_args(c, edgecolors, kwargs, xsize,
         - kwargs['edgecolor']
         - edgecolors (is an explicit kw argument in scatter())
         - kwargs['color'] (==kwcolor)
+        - c (if not None)
         - 'face' if not in classic mode else None
 
         Parameters
@@ -4357,7 +4360,7 @@ def _parse_scatter_color_args(c, edgecolors, kwargs, xsize,
         colors : array(N, 4) or None
             The facecolors as RGBA values, or *None* if a colormap is used.
         edgecolors
-            The edgecolor.
+            The edgecolor, or *None* if a colormap is used.
 
         """
         facecolors = kwargs.pop('facecolors', None)
@@ -4384,7 +4387,12 @@ def _parse_scatter_color_args(c, edgecolors, kwargs, xsize,
             if facecolors is None:
                 facecolors = kwcolor
 
-        if edgecolors is None and not mpl.rcParams['_internal.classic_mode']:
+        edge_from_c = edgecolors is None and c is not None
+
+        facecolors_none = cbook._str_lower_equal(facecolors, 'none')
+        if (edgecolors is None and not mpl.rcParams['_internal.classic_mode']
+                and (not edge_from_c or not facecolors_none)):
+
             edgecolors = mpl.rcParams['scatter.edgecolors']
 
         c_was_none = c is None
@@ -4435,6 +4443,8 @@ def invalid_shape_exception(csize, xsize):
         if not c_is_mapped:
             try:  # Is 'c' acceptable as PathCollection facecolors?
                 colors = mcolors.to_rgba_array(c)
+                if edge_from_c and facecolors is not None:
+                    edgecolors = mcolors.to_rgba_array(c)
             except (TypeError, ValueError) as err:
                 if "RGBA values should be within 0-1 range" in str(err):
                     raise
@@ -4453,6 +4463,8 @@ def invalid_shape_exception(csize, xsize):
                     raise invalid_shape_exception(len(colors), xsize)
         else:
             colors = None  # use cmap, norm after collection is created
+        if cbook._str_lower_equal(facecolors, 'none'):
+            colors = facecolors
         return c, colors, edgecolors
 
     @_preprocess_data(replace_names=["x", "y", "s", "linewidths",
@@ -4613,10 +4625,22 @@ def scatter(self, x, y, s=None, c=None, marker=None, cmap=None, norm=None,
                 c, edgecolors, kwargs, x.size,
                 get_next_color_func=self._get_patches_for_fill.get_next_color)
 
-        if plotnonfinite and colors is None:
+        if cmap and norm and not orig_edgecolor:
+            # override edgecolor based on cmap and norm presence
+            edgecolors = 'face'
+
+        if plotnonfinite and (colors is None and edgecolors is None):
+            c = np.ma.masked_invalid(c)
+            x, y, s, linewidths = \
+                cbook._combine_masks(x, y, s, linewidths)
+        elif plotnonfinite and colors is None:
             c = np.ma.masked_invalid(c)
             x, y, s, edgecolors, linewidths = \
                 cbook._combine_masks(x, y, s, edgecolors, linewidths)
+        elif plotnonfinite and edgecolors is None:
+            c = np.ma.masked_invalid(c)
+            x, y, s, colors, linewidths = \
+                cbook._combine_masks(x, y, s, colors, linewidths)
         else:
             x, y, s, c, colors, edgecolors, linewidths = \
                 cbook._combine_masks(
@@ -4690,7 +4714,9 @@ def scatter(self, x, y, s=None, c=None, marker=None, cmap=None, norm=None,
             alpha=alpha,
         )
         collection.set_transform(mtransforms.IdentityTransform())
-        if colors is None:
+
+        if ((colors is None or edgecolors is None) and not mcolors.is_color_like(c) and
+                (not isinstance(c, np.ndarray) or isinstance(c, np.ma.MaskedArray))):
             collection.set_array(c)
             collection.set_cmap(cmap)
             collection.set_norm(norm)

diff --git a/lib/matplotlib/tests/test_axes.py b/lib/matplotlib/tests/test_axes.py
@@ -2578,6 +2578,21 @@ def test_scatter_no_invalid_color(self, fig_test, fig_ref):
         ax = fig_ref.subplots()
         ax.scatter([0, 2], [0, 2], c=[1, 2], s=[1, 3], cmap=cmap)
 
+    @check_figures_equal(extensions=["png"])
+    def test_scatter_plotnonfinite_edgecolornone(self, fig_test, fig_ref):
+        ax = fig_test.subplots()
+        cmap = mpl.colormaps["viridis"].resampled(16)
+        cmap.set_bad("k", 1)
+        # Squelches warning in #25593 by testing a
+        # nonfinite plot with edgecolors set to None
+        ax.scatter(range(4), range(4),
+                   c=[1, np.nan, 2, np.nan], s=[1, 2, 3, 4],
+                   cmap=cmap, edgecolors=None, plotnonfinite=True)
+        ax = fig_ref.subplots()
+        cmap = mpl.colormaps["viridis"].resampled(16)
+        ax.scatter([0, 2], [0, 2], c=[1, 2], s=[1, 3], cmap=cmap)
+        ax.scatter([1, 3], [1, 3], s=[2, 4], color="k")
+
     def test_scatter_norm_vminvmax(self):
         """Parameters vmin, vmax should error if norm is given."""
         x = [1, 2, 3]
@@ -2749,6 +2764,8 @@ def get_next_color():
      (dict(c='b', edgecolor='r', edgecolors='g'), 'r'),
      (dict(color='r'), 'r'),
      (dict(color='r', edgecolor='g'), 'g'),
+     (dict(facecolors='none'), None),
+     (dict(c='b', facecolors='none'), np.array([[0, 0, 1, 1]]))
      ])
 def test_parse_scatter_color_args_edgecolors(kwargs, expected_edgecolors):
     def get_next_color():
@@ -2759,7 +2776,10 @@ def get_next_color():
     _, _, result_edgecolors = \
         mpl.axes.Axes._parse_scatter_color_args(
             c, edgecolors, kwargs, xsize=2, get_next_color_func=get_next_color)
-    assert result_edgecolors == expected_edgecolors
+    if isinstance(expected_edgecolors, np.ndarray):
+        assert_allclose(result_edgecolors, expected_edgecolors)
+    else:
+        assert result_edgecolors == expected_edgecolors
 
 
 def test_parse_scatter_color_args_error():