datetime_example.py

import datetime


def addseconds(timestamp, seconds):
    """Take timestamp as string and add seconds to it.

    >>> addseconds('00:01:45,667', 1)
    '00:01:46,667'
    >>> addseconds('00:01:45,667', 0.5)
    '00:01:46,167'
    """
    fmt = '%Y-%m-%d %H:%M:%S,%f'
    # American format requires dot instead of comma
    # Use datetime with a dummy date because datetime.time does not allow
    # adding or subtracting.
    x = datetime.datetime.strptime('2000-01-01 ' + timestamp, fmt)
    y = datetime.timedelta(seconds=seconds)
    x += y
    # Turn time component back into string
    newtimestamp = x.time().strftime('%H:%M:%S,%f')
    # strip off last three digits, and put comma back
    return newtimestamp[:-3]