Clarify error message for bad-dimensionality in pcolorfast().

Author: anntzer

lib/matplotlib/axes/_axes.py

@@ -6591,7 +6591,10 @@ def pcolorfast(self, *args, alpha=None, norm=None, cmap=None, vmin=None,
             elif x.ndim == 2 and y.ndim == 2:
                 style = "quadmesh"
             else:
-                raise TypeError("arguments do not match valid signatures")
+                raise TypeError(
+                    f"When 3 positional parameters are passed to pcolorfast, the first "
+                    f"two (X and Y) must be both 1D or both 2D; the given X was "
+                    f"{x.ndim}D and the given Y was {y.ndim}D")
         else:
             raise _api.nargs_error('pcolorfast', '1 or 3', len(args))
 

lib/matplotlib/tests/test_axes.py

@@ -6450,6 +6450,13 @@ def test_pcolorfast(xy, data, cls):
     assert type(ax.pcolorfast(*xy, data)) == cls
 
 
+def test_pcolorfast_bad_dims():
+    fig, ax = plt.subplots()
+    with pytest.raises(
+            TypeError, match=("the given X was 1D and the given Y was 2D")):
+        ax.pcolorfast(np.empty(6), np.empty((4, 7)), np.empty((8, 8)))
+
+
 def test_shared_scale():
     fig, axs = plt.subplots(2, 2, sharex=True, sharey=True)