nctn = open("nctn.txt").readlines()
nums = [int(n.strip()) for n in nctn]
nums = sorted(nums)

print(len(nums))

print(nums[:20])

def ranges(nums):
    '''Return a list of continuous ranges (min, max values) from a list of integers.'''
    
    rgs = [[nums[0]]]
    
    # these two make the code more readable and, incidentally, faster
    FIRST, LAST = 0, -1
    
    for n in nums:
        if rgs[LAST][LAST] == n - 1:
            if rgs[LAST][FIRST] == n -1:
                rgs[LAST].append(n)
            if rgs[LAST][FIRST] < n - 1:
                rgs[LAST][LAST] = n
        elif rgs[LAST][LAST] < n -1:
            rgs.append([n])
    return rgs

rgs = ranges(nums)
for r in rgs:
    try:
        print('{} - {}: {} numbers'.format(r[0], r[1], r[1] - r[0] + 1))
    except IndexError:
        print('{}: 1 number'.format(r[0]))

%timeit rgs = ranges(nums)