https://www.facebook.com/groups/utvecklare.stockholm/674230869292655/

open_hours.py

import datetime

FIRST_MONDAY = datetime.datetime(1970, 1, 5, tzinfo=datetime.timezone.utc).timestamp()

HOUR = 3600
DAY  = 24*HOUR
WEEK = 7*DAY

CLOSE_HOUR = 22
OPEN_HOUR  =  8

OPEN_DAYS_PER_WEEK = 5      # Monday - Friday

OPEN_HOURS_PER_DAY  = CLOSE_HOUR - OPEN_HOUR
OPEN_HOURS_PER_WEEK = OPEN_DAYS_PER_WEEK * OPEN_HOURS_PER_DAY

def primitive(ts):
    """
    Counting open hours (8:00 -- 22:00, Monday -- Friday) since first Monday after beginning of unix epoch
    """
    ts -= FIRST_MONDAY

    whole_weeks = ts // WEEK
    ts %= WEEK

    whole_days = ts // DAY
    if whole_days > OPEN_DAYS_PER_WEEK:
        whole_days = OPEN_DAYS_PER_WEEK
    ts %= DAY

    whole_hours = ts // HOUR
    whole_hours = whole_hours - OPEN_HOUR
    if whole_hours < 0:
        whole_hours = 0
    elif whole_hours > OPEN_HOURS_PER_DAY:
        whole_hours = OPEN_HOURS_PER_DAY

    return (
        whole_weeks * OPEN_HOURS_PER_WEEK +
        whole_days  * OPEN_HOURS_PER_DAY  +
        whole_hours
    )

def open_hours(ts_begin, ts_end):
    return primitive(ts_end) - primitive(ts_begin)




if __name__ == '__main__':
    ts_begin = datetime.datetime(2019, 1, 14, 12, 0, 0, tzinfo=datetime.timezone.utc) # Monday at 12.00
    ts_end   = datetime.datetime(2019, 1, 16, 17, 0, 0, tzinfo=datetime.timezone.utc) # Wednesday at 17.00
    print(open_hours(ts_begin.timestamp(), ts_end.timestamp()))
    # Two days + five hours = 2*14 + 5 = 33 hours