Calculating Time in Python (datetime.timedelta?)

I am sure this is a nobrainer for a lot of you, but I find myself really confused with the whole datetime.timedelta thing. Essentially I timestamp something when I start startTime and then I timestamp the end of the process endTime and I am trying to get the difference in HH:MM:SS and am having no luck.

I get this error when I do print endTime - startTime:

TypeError: unsupported operand type(s) for -: 'datetime.time' and 'datetime.time'

Edited to include final result:

startTime = datetime.now()
<... my looping process ...>
endTime = datetime.now()
calcdTime = endTime - startTime
print str(calcdTime)[:-4]

This outputs to: H:MM:SS.MM (thus stripping the last 4 characters off the timedelta