Python Programming

Coursera: Week 5

Kyria Kalokairi ♦ October 25, 2012 ♦ Leave a comment

Learn to Program: The Fundamentals 

Week 5 – while loops, lists, mutability

This week I learned that, of course, I’ve been doing it all wrong. Guido van Rossum has decided that there’s no room for individuality, and Python script must be standardized. To quote from Intermezzo: Coding Style: “Name your classes and functions consistently; the convention is to use CamelCase for classes and lower_case_with_underscores for functions and methods.”  To tell the truth, I was only using CamelCase because  I find underscoring to be unattractive. 

Only a couple of more weeks to go and I’m trying to put it all together. Since the first assignment involved modular arithmetic and 24-hour clocks, I thought I’d take the infamous ‘babysitter’ exercise and re-do it with a 12-hour clock. I guess I am a masochist.

Besides clock arithmetic it has Boolean expressions, if/elif statements, and exception handling. This is the one where I finally had to make friends with the debugger. I’m probably not done with it – it needs more input validation – but since there’s not a lot of code for clock arithmetic online (Python has its own built-in datetime module), I’m posting it anyway .

'''Ex 7. A babysitter charges $2.50 an hour until 9:00 PM when the rate drops
to $1.75 an hour (the children are in bed).
Write a program that accepts a starting time and ending time
in hours and minutes and calculates the total babysitting bill.
You may assume that the starting and ending times are in a single 24 hour period.
Partial hours should be appropriately prorated.'''

A = "Enter the time the sitter arrived in form HH:MM(specify AM or PM): "
B = "Enter the time the sitter left in form HH:MM (specify AM or PM): "
C = "Incorrect input. Please enter the time  the sitter arrived \
in form HH:MM(specify AM or PM): "
D = "Incorrect input. Please enter the time  the sitter left \
in form HH:MM(specify AM or PM): "

def calc_fee(start_time, end_time):
    '''
    str -> float

    Return the sitters fee by converting the given starting time
    and ending time into number of hours (in fractions)
    where noon = 12:00PM and midnight = 12:00AM.

    >>> calc_fee('3:45PM', '8:30PM')
    "The babysitter's fee is: $11.88"
    >>> calc_fee('9:10PM','11:40PM')
    "The babysitter's fee is: $4.38"
    >>> calc_fee('11:20AM','11:10PM')
    "The babysitter's fee is: $27.96"
    >>> calc_fee('9:20AM','11:10AM')
    "The babysitter's fee is: $4.58"
    >>> calc_fee('10:20AM','8:15PM')
    "The babysitter's fee is: $24.79"
    >>> calc_fee('12:40PM','11:50PM')
    "The babysitter's fee is: $25.79"
    >>> calc_fee('10:17AM','10:17PM')
    "The babysitter's fee is: $29.04"
    >>> calc_fee('11:00AM','12:00AM')
    "The babysitter's fee is: $30.25"
    >>> calc_fee('11:00AM','12:00PM')
    "The babysitter's fee is: $2.50"
    >>> calc_fee('10:15AM','11:15PM')
    "The babysitter's fee is: $30.81"
    '''

    #get AM or PM
    start_letter  = start_time[-2]
    end_letter = end_time[-2]

    #get the hours and minutes
    start_hour = eval(start_time.split(':')[0])
    end_hour = eval(end_time.split(':')[0])
    #convert minutes to decimal part of hour
    start_minutes = float(start_time[-4:-2])/60
    end_minutes = float(end_time[-4:-2])/60

    #modulo operation
    time = ((end_hour + end_minutes) - (start_hour + start_minutes))%12
    extra_hours = (end_hour + end_minutes) - 9.0

    # if hours = 12
    if time == 0:
        fee = 2.5*12.0
    # if 0 < hours < 12
    else:
        fee = 2.5*time

    #check if all hours after 9PM
    if start_letter == 'P'  and start_hour >= 9.0 and start_hour !=12:
        fee = fee*0.7
    #check if hours are more than 12 and end after 9PM
    elif end_hour != 12 and start_letter == 'A'\
      and end_letter == 'P' and end_hour > start_hour and end_hour >= 9.0:
        time = time + 12
        fee =  fee*time  - (0.75*(extra_hours))
    #check if hours are more than 12 and end before 9PM
    elif start_letter == 'A'  and end_letter == 'P'\
      and end_hour != 12 and end_hour > start_hour:
        time = time + 12
        fee = 2.5*time
    #check if hours end at midnight
    elif start_letter == 'A'  and end_letter == 'A'\
      and end_hour == 12 and end_hour > start_hour:
        time = time + 12
        fee = fee*time - (0.75*(extra_hours))
    #check for hours after 9PM
    elif  end_hour !=12 and  end_letter == 'P' and end_hour >= 9.0 :
        #subtract 0.75 cents/hour from fee after 9:00 PM
        fee =  fee - (0.75*(extra_hours))
    #check if hours ends at midnight
    elif end_hour == 12 and end_letter == 'A':
        fee =  fee*time - (0.75*(extra_hours))
    else:
        fee = fee

    return "The babysitter's fee is: $%.2f"% fee

def check_input():
    x = raw_input(A)
    y = raw_input(B)
    while True:
        try:
            print calc_fee(x,y)
            break
        except:
            x = raw_input(C)
            y = raw_input(D)

def main():
    check_input()
main()

if __name__ == "__main__":
    import doctest
    doctest.testmod()