This approach uses strptime and strftime with format directives as per https://docs.python.org/2/library/datetime.html#strftime-strptime-behavior, %H is the 24 hour clock, %I is the 12 hour clock and when using the 12 hour clock, %p qualifies if it is AM or PM.
>>> from datetime import datetime
>>> m2 = '1:35 PM'
>>> in_time = datetime.strptime(m2, "%I:%M %p")
>>> out_time = datetime.strftime(in_time, "%H:%M")
>>> print(out_time)
13:35