Adding a positive number and a negative number

In two’s complement representation, can adding one positive and one negative give you overflow? -- http://mail.python.org/mailman/listinfo/python-list

Swapping values of two variables

In python, I set: x=1 y=3 z = x x = y y = z This gave me 3 1, which are the values of x and y swapped. The following would have given me the same result: x, y = y, x But could the swapping be done using less extra memory than this? What is the minimum amount of extra memory required to exch