Python: Adding 3 weeks to any date

Question

I need help with a program.
How do I add 3 weeks (21 days) to any given date when the user can control the date?

The user will enter the date YYYY-MM-DD.

Below I'm trying to locate the hyphen and make sure there is only 2. This is what I have so far but all it does is repeat itself, can someone tell me where I went wrong ?:

date = raw_input("Enter date: ") i = 0 while i <= len(date):     if date[i] != "-":     i = i + 1 print date 

Now I'm picking out year, month, day. Is there an easier way to do this cause I need to account for the change months etc ?

year = date[0:4] month = date[5:7] day = date[9:11] 

thanks

Answer 1

Use datetime module to the task. You create a datetime aware object and add 21 days timedelta object to it.

>>> import datetime >>> u = datetime.datetime.strptime("2011-01-01","%Y-%m-%d") >>> d = datetime.timedelta(days=21) >>> t = u + d >>> print(t) 2011-01-22 00:00:00 

Answer 2

You can use a datetime.timedelta object to represent 3 weeks and then just add that to the datetime object that represents the user's input.

import datetime  date = raw_input("Enter date: ") aDate = datetime.datetime.strptime(date,"%Y-%m-%d") threeWeeks = datetime.timedelta(weeks = 3)  print aDate + threeWeeks 

See http://docs.python.org/library/datetime.html#strftime-and-strptime-behavior for details about using the strptime method.