Merge pull request matplotlib#23299 from tacaswell/enh/excludelist-on_rc_context

FIX/API: do not reset backend key in rc_context

Author: QuLogic

doc/api/next_api_changes/behavior/23299-TAC.rst

@@ -0,0 +1,6 @@
+mpl.rc_context no longer resets the value of ``'backend'``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+`matplotlib.rc_context` incorrectly reset the value of :rc:`backend` if backend
+resolution was triggered in the context. This affected only the value. The actual backend
+was not changed. Now, `matplotlib.rc_context` does not reset  :rc:`backend` anymore.

lib/matplotlib/__init__.py

@@ -1059,6 +1059,8 @@ def rc_context(rc=None, fname=None):
     """
     Return a context manager for temporarily changing rcParams.
 
+    The :rc:`backend` will not be reset by the context manager.
+
     Parameters
     ----------
     rc : dict
@@ -1087,7 +1089,8 @@ def rc_context(rc=None, fname=None):
              plt.plot(x, y)  # uses 'print.rc'
 
     """
-    orig = rcParams.copy()
+    orig = dict(rcParams.copy())
+    del orig['backend']
     try:
         if fname:
             rc_file(fname)

lib/matplotlib/tests/test_rcparams.py

@@ -496,6 +496,13 @@ def test_keymaps():
         assert isinstance(mpl.rcParams[k], list)
 
 
+def test_no_backend_reset_rccontext():
+    assert mpl.rcParams['backend'] != 'module://aardvark'
+    with mpl.rc_context():
+        mpl.rcParams['backend'] = 'module://aardvark'
+    assert mpl.rcParams['backend'] == 'module://aardvark'
+
+
 def test_rcparams_reset_after_fail():
     # There was previously a bug that meant that if rc_context failed and
     # raised an exception due to issues in the supplied rc parameters, the