datetime - How to add between two deltatime in python

Question

I have two string deltatime. I'm going to add two deltatime. There is unsupported operand "+" in Python. Is there any idea ?

delA = "00:45:34.563"

delB = "00:25:24.266"

a = datetime.datetime.strptime(delA, "%H:%M:%S.%f")

b = datetime.datetime.strptime(delB, "%H:%M:%S.%f")

print a, b
1900-01-01 00:45:34.563000 1900-01-01 00:25:24.266000

print a-b
0:20:10.297000

print a+b
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-43-31453f7268bc> in <module>()
----> 1 print a+b

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