jobdates.py

#!/usr/bin/env python

import datetime

class Job(object):
    def __init__(self, mean_hours, dates):
        self.mean_hours = mean_hours
        self.dates = dates

def parse_date(s):
    dt = datetime.datetime.strptime(s, '%Y-%m-%d')
    return datetime.date(dt.year, dt.month, dt.day)

def date_range(start, end):
    while start <= end:
        yield start
        start += datetime.timedelta(1)

jobs = [
    Job(4, date_range(parse_date('2016-02-04'), parse_date('2016-02-05'))),
    Job(8, date_range(parse_date('2016-02-05'), parse_date('2016-03-01'))),
]

for queried_date_s in ['2016-02-05', '2016-02-20']:
    queried_date = parse_date(queried_date_s)
    print('Hours for %s are %d' % (queried_date_s, sum([job.mean_hours for job in jobs if queried_date in job.dates])))

output.txt

Hours for 2016-02-05 are 12
Hours for 2016-02-20 are 8