Standardize signature mismatch error messages.

anntzer · anntzer · commit 72994f98c6da · 2020-03-13T11:26:11.000+01:00
This makes them consistent with the errors generated by Python for
"normal" functions.
diff --git a/doc/api/next_api_changes/behaviour.rst b/doc/api/next_api_changes/behaviour.rst
@@ -117,3 +117,8 @@ through it.
 This behavior is consistent with other figure saving methods
 (`.FigureCanvasAgg.print_png`, `.FigureCanvasPdf.print_pdf`,
 `.FigureCanvasSVG.print_svg`).
+
+`.pyplot.subplot()` now raises TypeError when given an incorrect number of arguments
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+This is consistent with other signature mismatch errors.  Previously a
+ValueError was raised.
diff --git a/lib/matplotlib/axes/_axes.py b/lib/matplotlib/axes/_axes.py
@@ -5519,8 +5519,8 @@ def _pcolorargs(funcname, *args, shading='flat'):
                     Y = Y.data
             nrows, ncols = C.shape
         else:
-            raise TypeError(
-                'Illegal arguments to %s; see help(%s)' % (funcname, funcname))
+            raise TypeError(f'{funcname}() takes 1 or 3 positional arguments '
+                            f'but {len(args)} were given')
 
         Nx = X.shape[-1]
         Ny = Y.shape[0]
diff --git a/lib/matplotlib/gridspec.py b/lib/matplotlib/gridspec.py
@@ -566,7 +566,8 @@ def _from_subplot_args(figure, args):
                 # num - 1 for converting from MATLAB to python indexing
                 return GridSpec(rows, cols, figure=figure)[int(num) - 1]
         else:
-            raise ValueError(f"Illegal argument(s) to subplot: {args}")
+            raise TypeError(f"subplot() takes 1 or 3 positional arguments but "
+                            f"{len(args)} were given")
 
     # num2 is a property only to handle the case where it is None and someone
     # mutates num1.
