If/Elif/Else Statements

Just like most other programming languages, Python includes the standard if, else-if, and else statements. The only difference is that Python's else-if statement is shortened to elif. The if statement checks for truth within a given condition. If the condition is false, the code within the if statement will not run. To counter this, you can use elif statements to check for further conditions. Finally we have the else statement which is a catch all if none of the previous statements evaluate to True.

Note: If even one statement is evaluated as true, all the remaining conditions will not be checked. Some situations call for multiple if statements, some work better with if/elif/else statements. Just keep in mind the order of the statements.

As mentioned in previous lectures, Python does not use brackets. So unlike C, Java, etc... Python uses indentation. To make this work for statements, loops, functions, etc... Python uses a colon ':' to declare the start of an indented block.

a = 100
if a > 100:
    print 'a is greater than 100'
elif a < 100:
    print 'a is less than 100'
else:
print 'a is equal to 100'

Output:

a is equal to 100

Another Example:

What is the output?

a = 0

# We will introduce while loops the right way, next lesson
while a <= 50:
    if a == 0:
        print "{} you can't divide by zero!".format(a)
    elif a % 10 == 0:
        print '{} can be divided by 10!!!'.format(a)
    elif a % 2 == 0:
        print '{} is even!'.format(a)
    else:
        print '{} is odd!'.format(a)
    a += 1