Range extraction

A format for expressing an ordered list of integers is to use a comma separated list of either

• individual integers
• Or a range of integers denoted by the starting integer separated from the end integer in the range by a dash, '-'. (The range includes all integers in the interval including both endpoints)

Range extraction
You are encouraged to solve this task according to the task description, using any language you may know.

So the list of integers: 1, 2, 3, 6, 7, 9 could be written as: 1-3,6-7,9 or as 1-3,6,7,9 or as ...

We add a further rule:

• The range syntax is to be used only for, and for every range that expands to more than two values.

This means that the above example could only become: 1-3,6,7,9

The task is to create a function that takes a list of integers and returns a correctly formatted string in the range format. Use the function to compute and print the range formatted version of the following ordered list of integers:

    0,  1,  2,  4,  6,  7,  8, 11, 12, 14,
   15, 16, 17, 18, 19, 20, 21, 22, 23, 24,
   25, 27, 28, 29, 30, 31, 32, 33, 35, 36,
   37, 38, 39

Python

<lang python>#import random

def rangeextract(lst):

   lenlst = len(lst)
   i, ranges = 0, []
   while i< lenlst:
       low = lst[i]
       while i <lenlst-1 and lst[i]+1 == lst[i+1]: i +=1
       hi = lst[i]
       ranges.append(
           '%i-%i'  % (low, hi) if hi - low >= 2 else
           ('%i,%i' % (low, hi) if hi - low == 1 else
            '%i' % low) )
       i += 1
   return ','.join(ranges)

1. lst = sorted(random.sample(list(range(40)), 33))
2. print (lst)

lst = [ 0, 1, 2, 4, 6, 7, 8, 11, 12, 14,

      15, 16, 17, 18, 19, 20, 21, 22, 23, 24,
      25, 27, 28, 29, 30, 31, 32, 33, 35, 36,
      37, 38, 39]

print(rangeextract(lst))</lang>