Reset style values on any error.

Author: chebee7i

lib/matplotlib/style/core.py

@@ -77,11 +77,11 @@ def use(style):
             try:
                 rc = rc_params_from_file(style, use_default_template=False)
                 mpl.rcParams.update(rc)
-            except:
+            except IOError:
                 msg = ("'%s' not found in the style library and input is "
                        "not a valid URL or path. See `style.available` for "
                        "list of available styles.")
-                raise ValueError(msg % style)
+                raise IOError(msg % style)
 
 
 @contextlib.contextmanager
@@ -111,9 +111,16 @@ def context(style, after_reset=False):
     initial_settings = mpl.rcParams.copy()
     if after_reset:
         mpl.rcdefaults()
-    use(style)
-    yield
-    mpl.rcParams.update(initial_settings)
+    try:
+        use(style)
+    except:
+        # Restore original settings before raising any errors during the update.
+        mpl.rcParams.update(initial_settings)
+        raise
+    else:
+        yield
+    finally:
+        mpl.rcParams.update(initial_settings)
 
 
 def load_base_library():

lib/matplotlib/tests/test_style.py

@@ -2,6 +2,7 @@
                         unicode_literals)
 
 import os
+import sys
 import shutil
 import tempfile
 from contextlib import contextmanager
@@ -12,6 +13,7 @@
 
 import six
 
+from nose.tools import assert_raises
 
 PARAM = 'image.cmap'
 VALUE = 'pink'
@@ -115,6 +117,22 @@ def test_context_with_union_of_dict_and_namedstyle():
     assert mpl.rcParams[other_param] == (not other_value)
 
 
+def test_context_with_badparam():
+    if sys.version_info[:2] >= (2, 7):
+        from collections import OrderedDict
+    else:
+        msg = "Test can only be run in Python >= 2.7 as it requires OrderedDict"
+        raise SkipTest(msg)
+
+    original_value = 'gray'
+    other_value = 'blue'
+    d = OrderedDict([(PARAM, original_value), ('badparam', None)])
+    with style.context({PARAM: other_value}):
+        assert mpl.rcParams[PARAM] == other_value
+        x = style.context([d])
+        assert_raises(KeyError, x.__enter__)
+        assert mpl.rcParams[PARAM] == other_value
+
 if __name__ == '__main__':
     from numpy import testing
     testing.run_module_suite()