def consecutivegaps(n, leftmargin = 0, rightmargin = 0):
    """Compute all possible single consecutive gaps in any sequence of the specified length. Returns
    (beginindex, length) tuples. Runs in  O(n(n+1) / 2) time. Argument is the length of the sequence rather than the sequence itself"""
    begin = leftmargin
    while begin < n:
        length = (n - rightmargin) - begin
        while length > 0:
            yield (begin, length)
            length -= 1
        begin += 1
Compute all possible single consecutive gaps in any sequence of the specified length. Returns
    (beginindex, length) tuples. Runs in  O(n(n+1) / 2) time. Argument is the length of the sequence rather than the sequence itself