How add a new orion node and setting it into existing polling engine

Here is some reference code for adding a node to a polling engine:

https://github.com/solarwinds/orionsdk-python/blob/master/samples/add_node.py

To specify which polling engine you want assign the node to, you would set the EngineID value here:

# set up property bag for the new node
props = {
    'IPAddress': ip_address,
    'EngineID': 1,
    'ObjectSubType': 'SNMP',
    'SNMPVersion': 2,
    'Community': community
}

You may also be interested in this code sample, which shows how to run the discovery process for a node:

https://github.com/solarwinds/orionsdk-python/blob/master/samples/discover_one_node.py