<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def statistics(self):
 """Return a dictionary of runtime statistics. This dictionary will be empty when the controller has never been ran. When it is running or has ran previously it should have (but may not) have useful and/or informational keys and values when running is underway and/or completed. .. warning:: The keys in this dictionary **should** be some what stable (not changing), but there existence **may** change between major releases as new statistics are gathered or removed so before accessing keys ensure that they actually exist and handle when they do not. .. note:: The values in this dictionary are local to the thread running call (so if multiple threads share the same retrying object - either directly or indirectly) they will each have there own view of statistics they have collected (in the future we may provide a way to aggregate the various statistics from each thread). """

        try:
            return self._local.statistics
        except AttributeError:
            self._local.statistics = {}
            return self._local.statistics