From 5c319e81d1f2fedb96c232c7c9e4532cce87babd Mon Sep 17 00:00:00 2001
From: Casey Brooks <casey.brooks@agyn.io>
Date: Thu, 25 Dec 2025 12:42:05 +0000
Subject: [PATCH] fix(pyplot): respect registered cmap key

---
 lib/matplotlib/pyplot.py            |  9 +++++---
 lib/matplotlib/tests/test_pyplot.py | 32 +++++++++++++++++++++++++++++
 2 files changed, 38 insertions(+), 3 deletions(-)

diff --git a/lib/matplotlib/pyplot.py b/lib/matplotlib/pyplot.py
index 58ce4c03fa87..4a919cdd4beb 100644
--- a/lib/matplotlib/pyplot.py
+++ b/lib/matplotlib/pyplot.py
@@ -2278,13 +2278,16 @@ def set_cmap(cmap: Colormap | str) -> None:
     matplotlib.cm.register_cmap
     matplotlib.cm.get_cmap
     """
-    cmap = get_cmap(cmap)
+    cmap_obj = get_cmap(cmap)
 
-    rc('image', cmap=cmap.name)
+    if isinstance(cmap, str):
+        rc('image', cmap=cmap)
+    else:
+        rc('image', cmap=cmap_obj.name)
     im = gci()
 
     if im is not None:
-        im.set_cmap(cmap)
+        im.set_cmap(cmap_obj)
 
 
 @_copy_docstring_and_deprecators(matplotlib.image.imread)
diff --git a/lib/matplotlib/tests/test_pyplot.py b/lib/matplotlib/tests/test_pyplot.py
index 16a927e9e154..1575be5a2f29 100644
--- a/lib/matplotlib/tests/test_pyplot.py
+++ b/lib/matplotlib/tests/test_pyplot.py
@@ -9,6 +9,7 @@
 import matplotlib as mpl
 from matplotlib.testing import subprocess_run_for_testing
 from matplotlib import pyplot as plt
+from matplotlib.colors import LinearSegmentedColormap
 
 
 def test_pyplot_up_to_date(tmpdir):
@@ -80,6 +81,37 @@ def test_stackplot_smoke():
     plt.stackplot([1, 2, 3], [1, 2, 3])
 
 
+def test_set_cmap_uses_registered_key_for_rcparams():
+    original_cmap = mpl.rcParams['image.cmap']
+    cmap = LinearSegmentedColormap.from_list(
+        'some_cmap_name', ['black', 'white']
+    )
+    mpl.colormaps.register(cmap, name='my_cmap_name', force=True)
+    try:
+        plt.set_cmap('my_cmap_name')
+        assert mpl.rcParams['image.cmap'] == 'my_cmap_name'
+        plt.imshow(np.arange(4).reshape(2, 2))
+    finally:
+        mpl.rcParams['image.cmap'] = original_cmap
+        mpl.colormaps.unregister('my_cmap_name')
+        plt.close('all')
+
+
+def test_set_cmap_colormap_object_rcparams_name_passthrough():
+    original_cmap = mpl.rcParams['image.cmap']
+    cmap = LinearSegmentedColormap.from_list(
+        'unregistered_internal_name', ['black', 'white']
+    )
+    mpl.colormaps.register(cmap, name='alias_for_object', force=True)
+    try:
+        plt.set_cmap(cmap)
+        assert mpl.rcParams['image.cmap'] == 'unregistered_internal_name'
+    finally:
+        mpl.rcParams['image.cmap'] = original_cmap
+        mpl.colormaps.unregister('alias_for_object')
+        plt.close('all')
+
+
 def test_nrows_error():
     with pytest.raises(TypeError):
         plt.subplot(nrows=1)