Support only positional args for data in contour

Author: chahak13

lib/matplotlib/contour.py

@@ -1386,7 +1386,7 @@ def _process_args(self, *args, corner_mask=None, algorithm=None, **kwargs):
         """
         Process args and kwargs.
         """
-        if isinstance(args[0], QuadContourSet):
+        if args and isinstance(args[0], QuadContourSet):
             if self.levels is None:
                 self.levels = args[0].levels
             self.zmin = args[0].zmin
@@ -1446,11 +1446,11 @@ def _contour_args(self, args, kwargs):
         else:
             fn = 'contour'
         nargs = len(args)
-        if nargs <= 2:
+        if 0 < nargs <= 2:
             z = ma.asarray(args[0], dtype=np.float64)
             x, y = self._initialize_x_y(z)
             args = args[1:]
-        elif nargs <= 4:
+        elif 2 < nargs <= 4:
             x, y, z = self._check_xyz(args[:3], kwargs)
             args = args[3:]
         else:

lib/matplotlib/tests/test_contour.py

@@ -693,3 +693,10 @@ def test_contour_remove():
     assert ax.get_children() != orig_children
     cs.remove()
     assert ax.get_children() == orig_children
+
+
+def test_contour_no_args():
+    fig, ax = plt.subplots()
+    data = [[0, 1], [1, 0]]
+    with pytest.raises(TypeError, match=r"contour\(\) takes from 1 to 4"):
+        ax.contour(Z=data)