Event_type paramter question

hello guys
I am fairly new to python programming and I am working through the tutorials and reading up online in other python resource sites. I got through the Control Servos tutorial and my code is working fine.
I went line by line trying to learn what it all meant and did however there is one line I am not understanding fully

I’m talking about the following line
If event_type == VC_CONTROLLER_END:

the reason I am confused is because I don’t see event_type being declared or used anywhere else in the program.

so I don’t understand where it’s getting it’s value from in order to compare it to the VC_CONTROLLER_END constant.

My other question related to this program is that VC_CONTROLLER_END constant what kind of value does it hold. string, numeric, object.

sorry if my questions seems a bit dumb like I said I am pretty new to python.

thanks in advance to anyone that can shed some light in the matter