need the average from a list of timedelta objects

I have created a list of timedelta objects and i need to get the average of this list. when i try to do

return (sum(delta_list)/(len(delta_list)-1))

i get

TypeError: unsupported operand type(s) for +: 'int' and 'datetime.timedelta'

I am new at working with python's datetime classes. I also would like to know how to get this average into a format like days: hours: mins: i don't need anything smaller than mins.