Don't revalidate rcParams when exiting rc_context.

anntzer · anntzer · commit cf42412b68ec · 2017-07-30T02:06:10.000-07:00
- Rewrite rc_context using contextmanager, which removes the need for
  saving state.

- When `__exit__`ing rc_context, skip rcParam validation, as the items
  have already been validated originally.

The rationale for not revalidating (beyond a minor gain in speed) is
that it may make sense to smuggle seemingly "invalid" values into the
rcParams (by calling `dict.__setitem__`), and we do not want them to
cause an error when exiting a rc_context (of course, they may or may not
cause an error at the backend level, but that is the responsibility of
whoever set this "invalid" value).

For example, the rcparam `lines.antialiased` is declared as a boolean,
but the mpl_cairo backend actually also recognizes any of cairo's
internal antialiasing enum values (NONE, FAST, GOOD, BEST, etc.).

(The rst docs needed to be slightly updated because .. autoclass::
rc_context won't work anymore, so I also took advantage of that to
reorder all the rc-related functions slightly more logically.)
diff --git a/doc/api/matplotlib_configuration_api.rst b/doc/api/matplotlib_configuration_api.rst
@@ -12,26 +12,24 @@ The top level :mod:`matplotlib` module
 
     An instance of :class:`RcParams` for handling default matplotlib values.
 
-.. autofunction:: rc
-
-.. autofunction::rcdefaults
-
-.. autofunction::rc_file
+.. autodata:: rc_context
 
-.. autofunction::rc_context
-
-.. autofunction:: matplotlib_fname
+.. autofunction:: rc
 
-.. autofunction::rc_file_defaults
+.. autofunction:: rc_file
 
-.. autofunction::interactive
+.. autofunction:: rcdefaults
 
-.. autofunction::is_interactive
+.. autofunction:: rc_file_defaults
 
 .. autoclass:: RcParams
 
 .. autofunction:: rc_params
 
 .. autofunction:: rc_params_from_file
 
-.. autoclass:: rc_context
+.. autofunction:: matplotlib_fname
+
+.. autofunction:: interactive
+
+.. autofunction:: is_interactive
diff --git a/lib/matplotlib/__init__.py b/lib/matplotlib/__init__.py
@@ -1222,7 +1222,8 @@ def rc_file(fname):
     rcParams.update(rc_params_from_file(fname))
 
 
-class rc_context(object):
+@contextlib.contextmanager
+def rc_context(rc=None, fname=None):
     """
     Return a context manager for managing rc settings.
 
@@ -1255,26 +1256,16 @@ class rc_context(object):
 
     """
 
-    def __init__(self, rc=None, fname=None):
-        self.rcdict = rc
-        self.fname = fname
-        self._rcparams = rcParams.copy()
-        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.clear()
-            rcParams.update(self._rcparams)
-            raise
-
-    def __enter__(self):
-        return self
-
-    def __exit__(self, type, value, tb):
-        rcParams.update(self._rcparams)
+    orig = rcParams.copy()
+    try:
+        if fname:
+            rc_file(fname)
+        if rc:
+            rcParams.update(rc)
+        yield
+    finally:
+        # No need to revalidate the original values.
+        dict.update(rcParams, orig)
 
 
 _use_error_msg = """
