python output unexpected behaviour

Following program is used to sort a list

    for i in range(len(q)):
        for j in range(len(q)):
            if not (q[i] < q[j]):
                t = q[i]
                q[i] = q[j]
                q[j] = t

contents of q are : {-1 2 4}

The output I get has one empty number like:

4

-1 2

i.e. extra number (empty) between 4 and -开发者_如何学JAVA1. What am I doing wrong?

You want to sort a list?

your_list.sort()