Avoid using deprecated ContourSet attributes (#5405)

docs/src/whatsnew/latest.rst

@@ -96,6 +96,9 @@ This document explains the changes made to Iris for this release
  `"Xarray bridge" <https://github.com/SciTools/iris/issues/4994>`_ facility.
  (:pull:`5214`)
 
+#. `@rcomer`_ updated :func:`~iris.plot.contourf` to avoid using functionality
+ that is deprecated in Matplotlib v3.8 (:pull:`5405`)
+
 
 
 .. comment

lib/iris/plot.py

@@ -1155,16 +1155,26 @@ def contourf(cube, *args, **kwargs):
  # But if the polygons are virtually opaque then we can cover the seams
  # by drawing anti-aliased lines *underneath* the polygon joins.
 
- # Figure out the alpha level for the contour plot
- if result.alpha is None:
- alpha = result.collections[0].get_facecolor()[0][3]
+ if hasattr(result, "get_antialiased"):
+ # Matplotlib v3.8 onwards.
+ antialiased = any(result.get_antialiased())
+ # Figure out the colours and alpha level for the contour plot
+ colors = result.get_facecolor()
+ alpha = result.alpha or colors[0][3]
+ # Define a zorder just *below* the polygons to ensure we minimise any boundary shift.
+ zorder = result.zorder - 0.1
  else:
- alpha = result.alpha
+ antialiased = result.antialiased
+ # Figure out the alpha level for the contour plot
+ alpha = result.alpha or result.collections[0].get_facecolor()[0][3]
+ colors = [c[0] for c in result.tcolors]
+ # Define a zorder just *below* the polygons to ensure we minimise any boundary shift.
+ zorder = result.collections[0].zorder - 0.1
+
  # If the contours are anti-aliased and mostly opaque then draw lines under
  # the seams.
- if result.antialiased and alpha > 0.95:
+ if antialiased and alpha > 0.95:
  levels = result.levels
- colors = [c[0] for c in result.tcolors]
  if result.extend == "neither":
  levels = levels[1:-1]
  colors = colors[:-1]
@@ -1177,11 +1187,7 @@ def contourf(cube, *args, **kwargs):
  else:
  colors = colors[:-1]
  if len(levels) > 0 and np.nanmax(cube.data) > levels[0]:
- # Draw the lines just *below* the polygons to ensure we minimise
- # any boundary shift.
- zorder = result.collections[0].zorder - 0.1
  axes = kwargs.get("axes", None)
-
  contour(
  cube,
  levels=levels,

lib/iris/tests/unit/plot/test_contourf.py

@@ -69,10 +69,8 @@ def setUp(self):
  self.bar_index = np.arange(self.bar.size)
  self.data = self.cube.data
  self.dataT = self.data.T
- mocker = mock.Mock(alpha=0, antialiased=False)
- self.mpl_patch = self.patch(
- "matplotlib.pyplot.contourf", return_value=mocker
- )
+ mocker = mock.Mock(wraps=plt.contourf)
+ self.mpl_patch = self.patch("matplotlib.pyplot.contourf", mocker)
  self.draw_func = iplt.contourf
 
 

lib/iris/tests/unit/quickplot/test_contourf.py

@@ -11,6 +11,7 @@
 
 from unittest import mock
 
+import matplotlib.pyplot as plt
 import numpy as np
 
 from iris.tests.stock import simple_2d
@@ -42,10 +43,8 @@ def setUp(self):
  self.bar_index = np.arange(self.bar.size)
  self.data = self.cube.data
  self.dataT = self.data.T
- mocker = mock.Mock(alpha=0, antialiased=False)
- self.mpl_patch = self.patch(
- "matplotlib.pyplot.contourf", return_value=mocker
- )
+ mocker = mock.Mock(wraps=plt.contourf)
+ self.mpl_patch = self.patch("matplotlib.pyplot.contourf", mocker)
  # Also need to mock the colorbar.
  self.patch("matplotlib.pyplot.colorbar")
  self.draw_func = qplt.contourf