How to get the first and last day of a week based on a date.

week_range.py

# coding: utf-8
"""
Sometimes we really need to get the first and the last date 
on a week, this function will help you to get this whatever 
day your week starts. 
"""
import datetime


MO, TU, WE, TH, FR, SA, SU = range(1, 8)


def week_range(dt, week_start=SU):
    """
    Find the first/last day of the week for the given day.

    Returns a tuple of ``(start_date, end_date)``.
    """
    # isocalendar calculates the year, week of the year, and day of the week.
    # dow is Mon = 1, ... Sat = 6, Sun = 7
    year, week, dow = dt.isocalendar()

    # Find the first day of the week.
    if dow == week_start:
        start_date = dt
    elif dow >= week_start:
        # subtract `dow` number days to get the first day
        start_date = dt - datetime.timedelta(days=dow - week_start)
    else:
        # subtract the `dow` to `week_start` and the week size to get the first day
        start_date = dt - datetime.timedelta(days=7 - (week_start - dow))

    # Now, add 6 for the last day of the week
    # (i.e., count up to Saturday if starts on Sunday)
    end_date = start_date + datetime.timedelta(6)

    return start_date, end_date