Python: Essential Reference, Third Edition

Conditionals

The if and else statements can perform simple tests. Here’s an example:

# Compute the maximum (z) of a and b
if a < b:
        z = b
else:
        z = a

The bodies of the if and else clauses are denoted by indentation. The else clause is optional.

To create an empty clause, use the pass statement as follows:

if a < b:
        pass      # Do nothing
else:
        z = a

You can form Boolean expressions by using the or, and, and not keywords:

if b >= a and b <= c:
        print "b is between a and c"
if not (b < a or b > c):
        print "b is still between a and c"

To handle multiple-test cases, use the elif statement, like this:

if a == '+':
        op = PLUS
elif a == '-':
        op = MINUS
elif a == '*':
        op = MULTIPLY
else:
        raise RuntimeError, "Unknown operator"

To denote truth values, you ...