[pinpoint] Docstrings for models/change/repository.py.

dashboard/dashboard/pinpoint/models/job.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 collections
 import logging
 import os
 import traceback
 
 from google.appengine.api import taskqueue
@@ skipping 231 matching lines @@
     For every pair of adjacent Changes, compare their results as probability
     distributions. If the results are different, find the midpoint of the
     Changes and add it to the Job.
 
     The midpoint can only be added if the second Change represents a commit that
     comes after the first Change. Otherwise, this method won't explore further.
     For example, if Change A is repo@abc, and Change B is repo@abc + patch,
     there's no way to pick additional Changes to try.
     """
     # This loop adds Changes to the _changes list while looping through it.
+    # The Change insertion simultaneously uses and modifies the list indices.
     # However, the loop index goes in reverse order and Changes are only added
     # after the loop index, so the loop never encounters the modified items.
     for index, change_b in reversed(tuple(self.Differences())):
       change_a = self._changes[index - 1]
 
       try:
         midpoint = change_module.Change.Midpoint(change_a, change_b)
       except change_module.NonLinearError:
         continue
 
@@ skipping 124 matching lines @@
 
   try:
     p_value = mann_whitney_u.MannWhitneyU(values_a, values_b)
   except ValueError:
     return _UNKNOWN
 
   if p_value < _SIGNIFICANCE_LEVEL:
     return _DIFFERENT
   else:
     return _UNKNOWN