Allows the client to get a hash map providing current value for any points which have changed since the last poll.
Requires SID of subscription whose values are being requested.
Returns hash mapping NID to current values for those values that have changed since the last poll was performed. The poll_changed function returns a hash of hashes. The returned value will contain the list of changed user specified node ID in the subscription manager(sid) and their respective hash values.
>>># Poll for changed values of Subscription, which is all values on first poll.
>>>sm.poll_changed(sid)
{'r1':{'cached': 1, 'timestamp': 1247088369.144726, 'changes': 1, 'value': 1}, 'r2': {'cached': 1, 'timestamp': 1247088369.150871, 'changes': 1, 'value': 0}, 'time': {'cached': 1, 'timestamp': 1247088369.155149, 'changes': 24, 'value': 1247088369.1551321}}
# Poll changed again, noting that the relay values are no longer present as they are unchanged.
sm.poll_changed(sid)
{'time': {'cached': 1, 'timestamp': 1247088398.897522, 'changes': 35, 'value': 1247088398.8975041}}