Replaces default value of shading from False to 'flat' in Quadmesh

Author: jeffreypaul15

lib/matplotlib/collections.py

@@ -2002,15 +2002,15 @@ def __init__(self, *args, **kwargs):
             # The following raises a TypeError iif the args don't match.
             w, h, coords, antialiased, shading, kwargs = (
                 lambda meshWidth, meshHeight, coordinates, antialiased=True,
-                       shading=False, **kwargs:
+                       shading='flat', **kwargs:
                 (meshWidth, meshHeight, coordinates, antialiased, shading,
                  kwargs))(*args, **kwargs)
         except TypeError as exc:
             # New signature:
             # If the following raises a TypeError (i.e. args don't match),
             # just let it propagate.
             coords, antialiased, shading, kwargs = (
-                lambda coordinates, antialiased=True, shading=False, **kwargs:
+                lambda coordinates, antialiased=True, shading='flat', **kwargs:
                 (coordinates, antialiased, shading, kwargs))(*args, **kwargs)
             coords = np.asarray(coords, np.float64)
         else:  # The old signature matched.

lib/matplotlib/tests/test_collections.py

@@ -744,6 +744,8 @@ def test_quadmesh_deprecated_signature(
     qmesh.set_array(C)
     ax.add_collection(qmesh)
 
+    assert qmesh._shading == 'flat'
+
     ax = fig_ref.add_subplot()
     ax.set(xlim=(0, 5), ylim=(0, 4))
     if 'transform' in kwargs: