How to extend datetime.timedelta?

Question

I am trying to extend the Python datetime.timedelta for use with cross country race results. I want to construct an object from a string in format u\"mm:s

Answer 1

Apparently timedelta objects are immutable, which means their value is actually set in the class' __new__() method—so you'll need to override that method instead of its __init__():

import datetime
import re

class RaceTimedelta(datetime.timedelta):
    def __new__(cls, timestr=''):
        m = re.match(r'(\d+):(\d+\.\d+)', timestr)
        if m:
            mins, secs = int(m.group(1)), float(m.group(2))
            return super(RaceTimedelta, cls).__new__(cls, minutes=mins, seconds=secs)
        else:
            raise ValueError('timestr argument not in format "mm:ss.d"')

print RaceTimedelta(u'24:45.7')

Output:

0:24:45.700000

BTW, I find it odd that you're providing a default value for thetimestrkeyword argument that will be considered illegal and raise aValueError.