import pymongo
from pymongo import MongoReplicaSetClient #, ReadPreference, MongoClient

This started when we changed over from MongoClient to support read preference in the near future:

Old:
#self.connection = MongoClient(MONGO_ALARMS_HOST, MONGO_PORT)

New:
self.connection = MongoReplicaSetClient(MONGO_HOST, replicaSet=MONGO_REPLICA_SET)

Dump:
AttributeError: 'NoneType' object has no attribute 'schedule_refresh'

Logger: root Level: error
Server: ip-10-2-53-250 First Seen: Oct. 31, 2013
Stacktrace (most recent call last):

(4 additional frame(s) were not displayed)
...
File "locations/views.py", line 928, in chart_png
x, y = statistics_dao.get_x_y_stats(location_id, key, start, end) # list objects have order, ok
File "statistics/statsDAO.py", line 154, in get_x_y_stats
for stat_datum in stats_data:

Exception (most recent call last)
AttributeError Root Cause
'NoneType' object has no attribute 'schedule_refresh'

locations/views.py ? in chart_png (application)

x, y = statistics_dao.get_x_y_stats(location_id, key, start, end) # list objects have order, ok
statistics/statsDAO.py ? in get_x_y_stats (application)

for stat_datum in stats_data:

We also always had a close:

    def __exit__(self, type, value, traceback):
        """needed for with"""
        #self.connection.end_request()
        self.connection.close()

I saw this issue being resolved in 2.5.1 I'll post a link to that issue