Handle multiple modifications to distribution metrics correctly.

infra_libs/ts_mon/common/errors.py

 # Copyright 2015 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.
 
 """Classes representing errors that can be raised by the monitoring library."""
 
 
 class MonitoringError(Exception):
   """Base class for exceptions raised by this module."""
 
 
 class MonitoringDecreasingValueError(MonitoringError):
   """Raised when setting a metric value that should increase but doesn't."""
 
   def __init__(self, metric, old_value, new_value):
-    self.metric = metric,
+    self.metric = metric
     self.old_value = old_value
     self.new_value = new_value
 
   def __str__(self):
     return ('Monotonically increasing metric "%s" was given value "%s", which '
             'is not greater than or equal to "%s".' % (
                 self.metric, self.new_value, self.old_value))
 
 
 class MonitoringDuplicateRegistrationError(MonitoringError):
@@ skipping 80 matching lines @@
 
 
 class UnknownModificationTypeError(MonitoringError):
   """Raised when using a Modification with an unknown type value."""
 
   def __init__(self, mod_type):
     self.mod_type = mod_type
 
   def __str__(self):
     return 'Unknown modification type "%s"' % self.mod_type