http://openbookproject.net/thinkcs/python/english3e/stacks.html

1. Apply the postfix algorithm to the expression 1 2 + 3 *.This example demonstrates one of the advantages of postfixthere is no need to use parentheses to control the order of operations. To get the same result in infix, we would have to write (1 + 2) * 3.

2. Write a postfix expression that is equivalent to 1 + 2 * 3.