Python Essential Reference, Second Edition

Conditionals

The if and else statements can perform simple tests. For 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"