Kata: Human readable duration format

README.md

Your task in order to complete this Kata is to write a function which formats a duration, given as a number of seconds, in a human-friendly way.

The function must accept a non-negative integer. If it is zero, it just returns "now". Otherwise, the duration is expressed as a combination of years, days, hours, minutes and seconds.

It is much easier to understand with an example:

  format_duration(62)    # returns "1 minute and 2 seconds"
  format_duration(3662)  # returns "1 hour, 1 minute and 2 seconds"

Note that spaces are important.

Detailed rules

The resulting expression is made of components like 4 seconds, 1 year, etc. In general, a positive integer and one of the valid units of time, separated by a space. The unit of time is used in plural if the integer is greater than 1.

The components are separated by a comma and a space (", "). Except the last component, which is separated by " and ", just like it would be written in English.

A more significant units of time will occur before than a least significant one. Therefore, 1 second and 1 year is not correct, but 1 year and 1 second is.

Different components have different unit of times. So there is not repeated units like in 5 seconds and 1 second.

A component will not appear at all if its value happens to be zero. Hence, 1 minute and 0 seconds is not valid, but it should be just 1 minute.

A unit of time must be used "as much as possible". It means that the function should not return 61 seconds, but 1 minute and 1 second instead. Formally, the duration specified by of a component must not be greater than any valid more significant unit of time.

For the purpose of this Kata, a year is 365 days and a day is 24 hours.

format_duration.py

def pluralize(n, word):
    if n == 1:
        return '%d %s' % (n, word)
        
    return '%d %ss' % (n, word)
        
def format_duration(seconds):
    if seconds == 0:
        return "now"
    
    ONE_MINUTE = 60
    ONE_HOUR = 60 * ONE_MINUTE
    ONE_DAY = 24 * ONE_HOUR
    ONE_YEAR = 365 * ONE_DAY
    
    units = (
        (ONE_YEAR, 'year'),
        (ONE_DAY, 'day'),
        (ONE_HOUR, 'hour'),
        (ONE_MINUTE, 'minute'),
        (1, 'second'),
    )
        
    r = []
    for unit in units:
        time_period, word = unit
        if seconds >= time_period:
            n = int(seconds / time_period)
            r.append(pluralize(n, word))
            seconds -= n * time_period
    
    return ' and'.join(', '.join(r).rsplit(',', 1))