Stop spy from handing a colormap to a Line2D (#814)

Author: cvanelteren

ultraplot/axes/plot.py

@@ -7700,11 +7700,18 @@ def spy(self, z, **kwargs):
         """
         kw = kwargs.copy()
         kw.update(_pop_props(kw, "line"))  # takes valid Line2D properties
-        default_cmap = pcolors.DiscreteColormap(["w", "k"], "_no_name")
-        center_levels = kw.pop("center_levels", None)
-        kw = self._parse_cmap(
-            z, center_levels=center_levels, default_cmap=default_cmap, **kw
-        )
+        # NOTE: Matplotlib's spy draws an image when no marker is given, and a
+        # Line2D of markers otherwise. Only the image understands a colormap, so
+        # parsing one for the marker path would hand 'cmap' to a Line2D.
+        markers = kw.get("marker", None) is not None or kw.get("markersize") is not None
+        if not markers:
+            default_cmap = pcolors.DiscreteColormap(["w", "k"], "_no_name")
+            center_levels = kw.pop("center_levels", None)
+            kw = self._parse_cmap(
+                z, center_levels=center_levels, default_cmap=default_cmap, **kw
+            )
+        else:
+            kw.pop("center_levels", None)
         guide_kw = _pop_params(kw, self._update_guide)
         m = self._call_native("spy", z, **kw)
         self._update_guide(m, queue_colorbar=False, **guide_kw)

ultraplot/tests/test_2dplots.py

@@ -453,6 +453,38 @@ def test_tripcolor_warns_when_z_and_facecolors_given():
         )
 
 
+def test_spy_marker_path_takes_no_colormap():
+    """
+    Marker-style spy must not be handed a colormap.
+
+    Matplotlib's spy draws an image when no marker is given and a Line2D of
+    markers otherwise; only the image understands `cmap`, so parsing one for
+    the marker path raised `Line2D.set() got an unexpected keyword argument`.
+    """
+    from matplotlib.image import AxesImage
+    from matplotlib.lines import Line2D
+
+    matrix = np.random.default_rng(51423).random((12, 12)) > 0.8
+    _, axs = uplt.subplots(ncols=4)
+    assert isinstance(axs[0].spy(matrix), AxesImage)
+    assert isinstance(axs[1].spy(matrix, markersize=2), Line2D)
+    assert isinstance(axs[2].spy(matrix, marker="s"), Line2D)
+    assert isinstance(axs[3].spy(matrix, color="denim", markersize=3), Line2D)
+
+
+def test_spy_image_path_still_takes_a_colormap():
+    """
+    The image path keeps its colormap handling, including the discrete default.
+    """
+    from matplotlib.image import AxesImage
+
+    matrix = np.random.default_rng(51423).random((12, 12)) > 0.8
+    _, ax = uplt.subplots()
+    image = ax.spy(matrix, cmap="Greys")
+    assert isinstance(image, AxesImage)
+    assert "greys" in image.get_cmap().name.lower()
+
+
 def test_tricontour_explicit_colors_match_levels():
     """
     Explicit triangular contour colors should map one-to-one with levels.