Improve error messages for mismatched s arg to scatter().

anntzer · anntzer · commit 2fc3ed6cae05 · 2025-12-11T18:05:06.000+01:00
- Display array sizes in case of size mismatch.
- Display a clearer, distinct error message when `s` is not real.
diff --git a/lib/matplotlib/axes/_axes.py b/lib/matplotlib/axes/_axes.py
@@ -5309,12 +5309,12 @@ def scatter(self, x, y, s=None, c=None, marker=None, cmap=None, norm=None,
             s = (20 if mpl.rcParams['_internal.classic_mode'] else
                  mpl.rcParams['lines.markersize'] ** 2.0)
         s = np.ma.ravel(s)
-        if (len(s) not in (1, x.size) or
-                (not np.issubdtype(s.dtype, np.floating) and
-                 not np.issubdtype(s.dtype, np.integer))):
-            raise ValueError(
-                "s must be a scalar, "
-                "or float array-like with the same size as x and y")
+        if not (np.issubdtype(s.dtype, np.floating)
+                or np.issubdtype(s.dtype, np.integer)):
+            raise ValueError(f"s must be float, but has type {s.dtype}")
+        if len(s) not in (1, x.size):
+            raise ValueError(f"s (size {len(s)}) cannot be broadcast "
+                             f"to match x and y (size {len(x)})")
 
         # get the original edgecolor the user passed before we normalize
         orig_edgecolor = edgecolors
diff --git a/lib/matplotlib/tests/test_axes.py b/lib/matplotlib/tests/test_axes.py
@@ -2958,11 +2958,11 @@ def test_scatter_unfillable(self):
 
     def test_scatter_size_arg_size(self):
         x = np.arange(4)
-        with pytest.raises(ValueError, match='same size as x and y'):
+        with pytest.raises(ValueError, match='cannot be broadcast to match x and y'):
             plt.scatter(x, x, x[1:])
-        with pytest.raises(ValueError, match='same size as x and y'):
+        with pytest.raises(ValueError, match='cannot be broadcast to match x and y'):
             plt.scatter(x[1:], x[1:], x)
-        with pytest.raises(ValueError, match='float array-like'):
+        with pytest.raises(ValueError, match='must be float'):
             plt.scatter(x, x, 'foo')
 
     def test_scatter_edgecolor_RGB(self):
