Range Updater

def update(mylist, row, col, cmprow, cmpcol):
    lo, hi = mylist[row][col]
    low, high = mylist[cmprow][cmpcol]

    # always replace the current value if it's (-1, -1)
    if (lo, hi) == (-1, -1):
        mylist[row][col] = low, high
        print "replacing empty", row, col, "with", cmprow, cmpcol
        return

    # never replace the current value if the ranges don't overlap
    # or the other range is (-1, -1)
    if (low, high) == (-1, -1) or lo >= high or hi <= low:
        print row, col, "doesn't overlap", cmprow, cmpcol
        return

    # set the low to the highest low and the high to the lowest high
    print "updating", row, col, "with", cmprow, cmpcol
    mylist[row][col] = max((lo, low)), min((hi, high))



def update_ranges(oldlist):
    # make a copy of the list as we're going to modify it
    mylist = oldlist[:]
    # we don't need the row titles, they just complicate things
    rowtitles, mylist = zip(*mylist)
    rows = len(mylist)
    columns = range(len(mylist[0]))

    # for each row except the last
    for i in xrange(rows - 1):
        # update it by going down all the rows below it
        for k in xrange(i+1, rows):
            # for both columns
            for j in columns:
                update(mylist, i, j, k, j)

    # put the row titles back in
    mylist = zip(rowtitles, mylist)
    return mylist



def test():
    oldlist = [ ('a', [ (-1, -1), (0.2, 0.4) ] ),
               ('b', [ (0.3, 1.0), (-1, -1) ] ),
               ('c', [ (-1, -1), (-1, -1) ] ),
               ('d', [ (0.15, 0.35), (0.05, 0.15) ] ) ]
    print "Original List"
    print '\n'.join(str(l) for l in oldlist)
    newlist = update_ranges(oldlist)
    print "New List"
    print '\n'.join(str(l) for l in newlist)

if __name__ == '__main__':
    test()