Interactive Brokers historical bars python example

I'm writing some code to get historical bar data from the IB through their API.

I've been using the resources at: https://interactivebrokers.github.io/tws-api/historical_bars.html

The problem is that in the example code, there is a datatype "BarData" that is never defined anywhere that I can find. Does anyone know how/where this needs to be defined? Is it supposed to be defined in "ibapi.client" or "ibapi.wrapper"?

Help?