SciTools · pp-mo · Sep 28, 2022 · Sep 28, 2022 · Sep 28, 2022 · Sep 28, 2022
diff --git a/benchmarks/benchmarks/import_iris.py b/benchmarks/benchmarks/import_iris.py
@@ -5,10 +5,30 @@
 # licensing details.
 from importlib import import_module, reload
 
+################
+# Prepare info for reset_colormaps:
+
+# Import and capture colormaps.
+from matplotlib import colormaps  # isort:skip
+
+_COLORMAPS_ORIG = set(colormaps)
+
+# Import iris.palette, which modifies colormaps.
+import iris.palette
+
+# Derive which colormaps have been added by iris.palette.
+_COLORMAPS_MOD = set(colormaps)
+COLORMAPS_EXTRA = _COLORMAPS_MOD - _COLORMAPS_ORIG
+
+# Touch iris.palette to prevent linters complaining.
+_ = iris.palette
+
+################
+
 
 class Iris:
     @staticmethod
-    def _import(module_name):
+    def _import(module_name, reset_colormaps=False):
         """
         Have experimented with adding sleep() commands into the imported
         modules. The results reveal:
@@ -25,6 +45,13 @@ def _import(module_name):
         and the repetitions are therefore no faster than the first run.
         """
         mod = import_module(module_name)
+
+        if reset_colormaps:
+            # Needed because reload() will attempt to register new colormaps a
+            #  second time, which errors by default.
+            for cm_name in COLORMAPS_EXTRA:
+                colormaps.unregister(cm_name)
+
         reload(mod)
 
     def time_iris(self):
@@ -205,7 +232,7 @@ def time_iterate(self):
         self._import("iris.iterate")
 
     def time_palette(self):
-        self._import("iris.palette")
+        self._import("iris.palette", reset_colormaps=True)
 
     def time_plot(self):
         self._import("iris.plot")

diff --git a/docs/src/whatsnew/latest.rst b/docs/src/whatsnew/latest.rst
@@ -83,14 +83,20 @@ This document explains the changes made to Iris for this release
 
 #. `@rcomer`_ introduced the ``dask >=2.26`` minimum pin, so that Iris can benefit
    from Dask's support for `NEP13`_ and `NEP18`_. (:pull:`4905`)
+
 #. `@trexfeathers`_ advanced the Cartopy pin to ``>=0.21``, as Cartopy's
    change to default Transverse Mercator projection affects an Iris test.
    See `SciTools/cartopy@fcb784d`_ and `SciTools/cartopy@8860a81`_ for more
    details.
    (:pull:`4968`)
+
 #. `@trexfeathers`_ introduced the ``netcdf4!=1.6.1`` pin to avoid a problem
    with segfaults. (:pull:`4968`)
 
+#. `@trexfeathers`_ updated the Matplotlib colormap registration in
+   :mod:`iris.palette` in response to a deprecation warning. Using the new
+   Matplotlib API also means a ``matplotlib>=3.5`` pin. (:pull:`4998`)
+
 
 📚 Documentation
 ================
@@ -114,6 +120,9 @@ This document explains the changes made to Iris for this release
    :mod:`~iris.fileformats.netcdf.loader` and :mod:`~iris.fileformats.netcdf.saver`
    submodules, just to make the code easier to handle.
 
+#. `@trexfeathers`_ adapted the benchmark for importing :mod:`iris.palette` to
+   cope with new colormap behaviour in Matplotlib `v3.6`. (:pull:`4998`)
+
 
 .. comment
     Whatsnew author names (@github name) in alphabetical order. Note that,

diff --git a/lib/iris/palette.py b/lib/iris/palette.py
@@ -15,6 +15,7 @@
 import re
 
 import cf_units
+from matplotlib import colormaps as mpl_colormaps
 import matplotlib.cm as mpl_cm
 import matplotlib.colors as mpl_colors
 import numpy as np
@@ -337,7 +338,7 @@ def _load_palette():
             )
 
         # Register the color map for use.
-        mpl_cm.register_cmap(cmap=cmap)
+        mpl_colormaps.register(cmap)
 
 
 # Ensure to load the color map palettes.

diff --git a/requirements/ci/py310.yml b/requirements/ci/py310.yml
@@ -15,7 +15,7 @@ dependencies:
   - cf-units >=3.1
   - cftime >=1.5
   - dask-core >=2.26
-  - matplotlib
+  - matplotlib >=3.5
   - netcdf4 !=1.6.1
   - numpy >=1.19
   - python-xxhash

diff --git a/requirements/ci/py38.yml b/requirements/ci/py38.yml
@@ -15,7 +15,7 @@ dependencies:
   - cf-units >=3.1
   - cftime >=1.5
   - dask-core >=2.26
-  - matplotlib
+  - matplotlib >=3.5
   - netcdf4 !=1.6.1
   - numpy >=1.19
   - python-xxhash

diff --git a/requirements/ci/py39.yml b/requirements/ci/py39.yml
@@ -15,7 +15,7 @@ dependencies:
   - cf-units >=3.1
   - cftime >=1.5
   - dask-core >=2.26
-  - matplotlib
+  - matplotlib >=3.5
   - netcdf4 !=1.6.1
   - numpy >=1.19
   - python-xxhash

diff --git a/setup.cfg b/setup.cfg
@@ -51,7 +51,7 @@ install_requires =
     cf-units>=3.1
     cftime>=1.5.0
     dask[array]>=2.26
-    matplotlib
+    matplotlib>=3.5
     netcdf4!=1.6.1
     numpy>=1.19
     scipy