Fix incorrect usage of nargs_error.

nargs_error simply returns the exception, the caller needs to throw it.

Author: anntzer

lib/matplotlib/axes/_axes.py

@@ -321,7 +321,7 @@ def legend(self, *args, **kwargs):
                 *args,
                 **kwargs)
         if len(extra_args):
-            _api.nargs_error('legend', '0-2', len(args))
+            raise _api.nargs_error('legend', '0-2', len(args))
         self.legend_ = mlegend.Legend(self, handles, labels, **kwargs)
         self.legend_._remove_method = self._remove_legend
         return self.legend_
@@ -3005,7 +3005,7 @@ def stem(self, *args, linefmt=None, markerfmt=None, basefmt=None, bottom=0,
             which inspired this method.
         """
         if not 1 <= len(args) <= 3:
-            _api.nargs_error('stem', '1-3', len(args))
+            raise _api.nargs_error('stem', '1-3', len(args))
         _api.check_in_list(['horizontal', 'vertical'], orientation=orientation)
 
         if len(args) == 1:
@@ -6422,7 +6422,7 @@ def pcolorfast(self, *args, alpha=None, norm=None, cmap=None, vmin=None,
             else:
                 raise TypeError("arguments do not match valid signatures")
         else:
-            _api.nargs_error('pcolorfast', '1 or 3', len(args))
+            raise _api.nargs_error('pcolorfast', '1 or 3', len(args))
 
         if style == "quadmesh":
             # data point in each cell is value at lower left corner

lib/matplotlib/rcsetup.py

@@ -693,7 +693,7 @@ def cycler(*args, **kwargs):
     elif len(args) == 2:
         pairs = [(args[0], args[1])]
     elif len(args) > 2:
-        _api.nargs_error('cycler', '0-2', len(args))
+        raise _api.nargs_error('cycler', '0-2', len(args))
     else:
         pairs = kwargs.items()