Getting the date of the first day of the week

To get the beginning date of the week from Sunday:

datetime.today() - datetime.timedelta(days=datetime.today().isoweekday() % 7)

Thanks @PavSidhu and editors of that answer. Building further on that answer:

If your start of week is Sunday

import datetime
datetime.datetime.today() - datetime.timedelta(days=datetime.datetime.today().isoweekday() % 7)

If your start of week is Monday

import datetime
datetime.datetime.today()  - datetime.timedelta(days=datetime.datetime.today().weekday() % 7)

If you want to calculate start of week for a future date

import datetime
from dateutil.relativedelta import relativedelta

# 5 days ahead of today
future_date = datetime.datetime.today() + relativedelta(days=5)

# If Start of Week is Monday
print(future_date - datetime.timedelta(days=future_date.weekday() % 7))

# If start of week is Sunday
print(future_date - datetime.timedelta(days=future_date.isoweekday() % 7))

Diff: When start of week is Monday, we are using weekday() instead of isoweekday()

• isoweekday() - Monday is 1 and Sunday is 7
• weekday() - Monday is 0 and Sunday is 6