Apply suggestions from code review

Co-authored-by: Mathias Hauser <mathause@users.noreply.github.com>

Author: johnomotani

xarray/plot/plot.py

@@ -651,16 +651,14 @@ def newplotfunc(
         if subplot_kws is None:
             subplot_kws = dict()
 
-        if "surface" == plotfunc.__name__ and not kwargs.get("_is_facetgrid", False):
+        if plotfunc.__name__ == "surface" and not kwargs.get("_is_facetgrid", False):
             # Check we have new enough version of matplotlib
             from distutils.version import LooseVersion
 
             import matplotlib as mpl
 
             if LooseVersion(mpl.__version__) < "3.2.0":
                 raise ValueError("surface plot requires at least matplotlib-3.2.0")
-            del LooseVersion
-            del mpl
 
             if ax is None:
                 # Need to create a "3d" Axes instance for surface plots
@@ -683,7 +681,7 @@ def newplotfunc(
         plt = import_matplotlib_pyplot()
 
         if (
-            "surface" == plotfunc.__name__
+            plotfunc.__name__ == "surface"
             and not kwargs.get("_is_facetgrid", False)
             and ax is not None
         ):

xarray/tests/test_plot.py

@@ -135,7 +135,8 @@ def setup(self):
         # Remove all matplotlib figures
         plt.close("all")
 
-    def pass_in_axis(self, plotmethod, subplot_kw={}):
+    def pass_in_axis(self, plotmethod, subplot_kw=None):
+        subplot_kw = {} if subplot_kw is None else subplot_kw
         fig, axes = plt.subplots(ncols=2, subplot_kw=subplot_kw)
         plotmethod(ax=axes[0])
         assert axes[0].has_data()