[Culprit-Finder] Add generator cache decorator.

appengine/findit/crash/loglinear/changelist_features/min_distance.py

 # Copyright 2016 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import logging
 import math
 
 from crash.loglinear.feature import ChangedFile
 from crash.loglinear.feature import Feature
 from crash.loglinear.feature import FeatureValue
@@ skipping 55 matching lines @@
         message = 'No AnalysisInfo for any file in suspect: %s' % str(suspect)
         logging.warning(message)
         return FeatureValue(self.name, lmath.LOG_ZERO, message, None)
 
       min_distance = min(per_file_analysis.min_distance
                          for per_file_analysis in analyses.itervalues())
 
       return FeatureValue(
           name = self.name,
           value = LogLinearlyScaled(float(min_distance), float(self._maximum)),
-          reason = ('Minimum distance is %d' % min_distance),
+          reason = ('Minimum distance is %d' % min_distance
+                    if not math.isinf(min_distance) else
+                    'Minimum distance is infinity'),
           changed_files = self._ChangedFiles(suspect),
       )
 
     return FeatureValueGivenReport
 
   def _ChangedFiles(self, suspect):
     """Get all the changed files causing this feature to blame this suspect.
 
     Arg:
       suspect (Suspect): the suspect being blamed.
@@ skipping 31 matching lines @@
       )
 
     if not index_to_changed_files: # pragma: no cover
       logging.warning('Found no changed files for suspect: %s', str(suspect))
 
     # Sort changed file by frame index.
     _, changed_files = zip(*sorted(index_to_changed_files.items(),
                                    key=lambda x: x[0]))
 
     return list(changed_files)