Fixed a bug that caused rc parameters to not be reset to initial state if an exception happened while setting new rc parameters inside rc_context.

astrofrog · astrofrog · commit bc00dc9f8ee8 · 2014-11-02T15:16:10.000+01:00
diff --git a/lib/matplotlib/__init__.py b/lib/matplotlib/__init__.py
@@ -1249,10 +1249,15 @@ def __init__(self, rc=None, fname=None):
         self.rcdict = rc
         self.fname = fname
         self._rcparams = rcParams.copy()
-        if self.fname:
-            rc_file(self.fname)
-        if self.rcdict:
-            rcParams.update(self.rcdict)
+        try:
+            if self.fname:
+                rc_file(self.fname)
+            if self.rcdict:
+                rcParams.update(self.rcdict)
+        except:
+            # if anything goes wrong, revert rc parameters and re-raise
+            rcParams.update(self._rcparams)
+            raise
 
     def __enter__(self):
         return self
diff --git a/lib/matplotlib/tests/test_rcparams.py b/lib/matplotlib/tests/test_rcparams.py
@@ -262,3 +262,25 @@ def test_keymaps():
     key_list = [k for k in mpl.rcParams if 'keymap' in k]
     for k in key_list:
         assert(isinstance(mpl.rcParams[k], list))
+
+
+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
+    # global rc parameters were left in a modified state.
+
+    try:
+        from collections import OrderedDict
+    except:
+        return  # can't run this test on Python 2.6
+
+    with mpl.rc_context(rc={'text.usetex': False}):
+
+        assert mpl.rcParams['text.usetex'] is False
+
+        with assert_raises(KeyError):
+            with mpl.rc_context(rc=OrderedDict([('text.usetex', True),('test.blah', True)])):
+                pass
+
+        assert mpl.rcParams['text.usetex'] is False
