consecutive_dates.py

# I only have such long documentation on consecutive_date_ranges to run doctest.

from collections import namedtuple

DateRange = namedtuple('DateRange', 'start end length')

def is_after(lhs, rhs):
    return lhs == rhs + 1

def consecutive_date_ranges(dates):
    """Given a list of dates, output a list of ranges of consecutive dates in the input.

    >>> consecutive_date_ranges([])
    []

    >>> consecutive_date_ranges([8])
    [DateRange(start=8, end=8, length=0)]

    >>> consecutive_date_ranges([1, 4, 2, 7, 9, 8])
    [DateRange(start=1, end=2, length=1), DateRange(start=4, end=4, length=0), DateRange(start=7, end=9, length=2)]

    >>> consecutive_date_ranges([1, 4, 7, 9, 8])
    [DateRange(start=1, end=1, length=0), DateRange(start=4, end=4, length=0), DateRange(start=7, end=9, length=2)]

    >>> consecutive_date_ranges([1, 4, 2, 11])
    [DateRange(start=1, end=2, length=1), DateRange(start=4, end=4, length=0), DateRange(start=11, end=11, length=0)]

    >>> consecutive_date_ranges([1, 2, 3, 4, 5])
    [DateRange(start=1, end=5, length=4)]
    """

    dates = sorted(dates)

    range_starts = [date for i, date in enumerate(dates)
                    if i == 0 or not is_after(date, dates[i - 1])]

    range_ends = [date for i, date in enumerate(dates)
                  if i == len(dates) - 1 or not is_after(dates[i + 1], date)]

    return [DateRange(start, end, end - start)
            for start, end in zip(range_starts, range_ends)]

Don't know why I got in such a Ramda pipe: https://repl.it/repls/SplendidYellowishGlitch