plt.gca() no longer accepts kwargs (#5450)

* plt.gca() no longer accepts kwargs

* use gcf unconditionally

Author: mathause

xarray/plot/utils.py

@@ -441,11 +441,26 @@ def get_axis(figsize=None, size=None, aspect=None, ax=None, **kwargs):
         raise ValueError("cannot use subplot_kws with existing ax")
 
     if ax is None:
-        ax = plt.gca(**kwargs)
+        ax = _maybe_gca(**kwargs)
 
     return ax
 
 
+def _maybe_gca(**kwargs):
+
+    import matplotlib.pyplot as plt
+
+    # can call gcf unconditionally: either it exists or would be created by plt.axes
+    f = plt.gcf()
+
+    # only call gca if an active axes exists
+    if f.axes:
+        # can not pass kwargs to active axes
+        return plt.gca()
+
+    return plt.axes(**kwargs)
+
+
 def label_from_attrs(da, extra=""):
     """Makes informative labels if variable metadata (attrs) follows
     CF conventions."""

xarray/tests/test_plot.py

@@ -17,6 +17,7 @@
     _build_discrete_cmap,
     _color_palette,
     _determine_cmap_params,
+    _maybe_gca,
     get_axis,
     label_from_attrs,
 )
@@ -2777,3 +2778,31 @@ def test_get_axis_cartopy():
     with figure_context():
         ax = get_axis(**kwargs)
         assert isinstance(ax, cartopy.mpl.geoaxes.GeoAxesSubplot)
+
+
+@requires_matplotlib
+def test_maybe_gca():
+
+    with figure_context():
+        ax = _maybe_gca(aspect=1)
+
+        assert isinstance(ax, mpl.axes.Axes)
+        assert ax.get_aspect() == 1
+
+    with figure_context():
+
+        # create figure without axes
+        plt.figure()
+        ax = _maybe_gca(aspect=1)
+
+        assert isinstance(ax, mpl.axes.Axes)
+        assert ax.get_aspect() == 1
+
+    with figure_context():
+        existing_axes = plt.axes()
+        ax = _maybe_gca(aspect=1)
+
+        # re-uses the existing axes
+        assert existing_axes == ax
+        # kwargs are ignored when reusing axes
+        assert ax.get_aspect() == "auto"