days_between_dates.py

class Date:
    def __init__(self, day, month, year):
        self.day = day
        self.month = month
        self.year = year

my_birthday = Date(16, 4, 1991)
today = Date(28, 6, 1991)

def make_days_of_months(is_leap_year):
    days_of_months = [ 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 ]
    if is_leap_year:
        days_of_months[1] = 29
    return days_of_months

def is_leap_year(year):
    if year % 4. != 0.:
        return False
    elif year % 100 != 0:
        return True
    elif year % 400 != 0:
        return False
    else:
        return True

def calculate_completed_year_days(date):
    days_of_month = make_days_of_months(is_leap_year(date.year))
    
    completed_days = date.day
    for month in range(0, date.month - 1):
        completed_days += days_of_month[month]
    
    return completed_days

def total_days_in_year(year):
    if is_leap_year(year):
        return 366

    return 365

def days_between_dates(start, end):
    initial_date_completed_days = calculate_completed_year_days(start)
    final_date_completed_days = calculate_completed_year_days(end)

    if start.year == end.year:
        return final_date_completed_days - initial_date_completed_days

    total_days = 0
    for year in range(start.year + 1, end.year):
        total_days += total_days_in_year(year)

    total_days = total_days +\
        (total_days_in_year(start.year) - initial_date_completed_days) +\
        final_date_completed_days
    return total_days

print(days_between_dates(my_birthday, today))