TST: Address MPL 3.6 deprecation warnings (#48695)

* TST: Address MPL 3.6 deprecation warnings

* Address min build

* missing ()

pandas/io/formats/style.py

@@ -3934,7 +3934,15 @@ def _background_gradient(
         rng = smax - smin
         # extend lower / upper bounds, compresses color range
         norm = mpl.colors.Normalize(smin - (rng * low), smax + (rng * high))
-        rgbas = plt.cm.get_cmap(cmap)(norm(gmap))
+        from pandas.plotting._matplotlib.compat import mpl_ge_3_6_0
+
+        if mpl_ge_3_6_0():
+            if cmap is None:
+                rgbas = mpl.colormaps[mpl.rcParams["image.cmap"]](norm(gmap))
+            else:
+                rgbas = mpl.colormaps[cmap](norm(gmap))
+        else:
+            rgbas = plt.cm.get_cmap(cmap)(norm(gmap))
 
         def relative_luminance(rgba) -> float:
             """
@@ -4213,8 +4221,10 @@ def css_calc(x, left: float, right: float, align: str, color: str | list | tuple
     if cmap is not None:
         # use the matplotlib colormap input
         with _mpl(Styler.bar) as (plt, mpl):
+            from pandas.plotting._matplotlib.compat import mpl_ge_3_6_0
+
             cmap = (
-                mpl.cm.get_cmap(cmap)
+                (mpl.colormaps[cmap] if mpl_ge_3_6_0() else mpl.cm.get_cmap(cmap))
                 if isinstance(cmap, str)
                 else cmap  # assumed to be a Colormap instance as documented
             )

pandas/tests/io/formats/style/test_matplotlib.py

@@ -13,6 +13,7 @@
 import matplotlib as mpl
 
 from pandas.io.formats.style import Styler
+from pandas.plotting._matplotlib.compat import mpl_ge_3_6_0
 
 
 @pytest.fixture
@@ -260,7 +261,10 @@ def test_background_gradient_gmap_wrong_series(styler_blank):
         styler_blank.background_gradient(gmap=gmap, axis=None)._compute()
 
 
-@pytest.mark.parametrize("cmap", ["PuBu", mpl.cm.get_cmap("PuBu")])
+@pytest.mark.parametrize(
+    "cmap",
+    ["PuBu", mpl.colormaps["PuBu"] if mpl_ge_3_6_0() else mpl.cm.get_cmap("PuBu")],
+)
 def test_bar_colormap(cmap):
     data = DataFrame([[1, 2], [3, 4]])
     ctx = data.style.bar(cmap=cmap, axis=None)._compute().ctx

pandas/tests/plotting/common.py

@@ -479,25 +479,29 @@ def is_grid_on():
             mpl.rc("axes", grid=False)
             obj.plot(kind=kind, **kws)
             assert not is_grid_on()
+            self.plt.clf()
 
             self.plt.subplot(1, 4 * len(kinds), spndx)
             spndx += 1
             mpl.rc("axes", grid=True)
             obj.plot(kind=kind, grid=False, **kws)
             assert not is_grid_on()
+            self.plt.clf()
 
             if kind not in ["pie", "hexbin", "scatter"]:
                 self.plt.subplot(1, 4 * len(kinds), spndx)
                 spndx += 1
                 mpl.rc("axes", grid=True)
                 obj.plot(kind=kind, **kws)
                 assert is_grid_on()
+                self.plt.clf()
 
                 self.plt.subplot(1, 4 * len(kinds), spndx)
                 spndx += 1
                 mpl.rc("axes", grid=False)
                 obj.plot(kind=kind, grid=True, **kws)
                 assert is_grid_on()
+                self.plt.clf()
 
     def _unpack_cycler(self, rcParams, field="color"):
         """