converting a list of integers into range in python

Question

Is there something existing in python that can convert an increasing list of integers into a range list

E.g. given the set {0, 1, 2, 3, 4, 7, 8, 9, 11} I want to get

Answer 1

Generating range pairs:

def ranges(lst):
    s = e = None
    r = []
    for i in sorted(lst):
        if s is None:
            s = e = i
        elif i == e or i == e + 1:
            e = i
        else:
            r.append((s, e))
            s = e = i
    if s is not None:
        r.append((s, e))
    return r

Example:

>>> lst = [1, 5, 6, 7, 12, 15, 16, 17, 18, 30]
>>> print repr(ranges(lst))
[(1, 1), (5, 7), (12, 12), (15, 18), (30, 30)]

As a generator:

def gen_ranges(lst):
    s = e = None
    for i in sorted(lst):
        if s is None:
            s = e = i
        elif i == e or i == e + 1:
            e = i
        else:
            yield (s, e)
            s = e = i
    if s is not None:
        yield (s, e)

Example:

>>> lst = [1, 5, 6, 7, 12, 15, 16, 17, 18, 30]
>>> print repr(','.join(['%d' % s if s == e else '%d-%d' % (s, e) for (s, e) in gen_ranges(lst)]))
'1,5-7,12,15-18,30'