Lesson 02-08: If/Else Statements¶

The else Keyword¶

When you use if statements, you are testing to see if a boolean condition is True. What if you wanted to execute some code if it is True, but to also execute some code if it is False? While you could use the following code:

if condition:
    #do stuff
if not condition:
    #do other stuff

...it would be inefficient and difficult to read. There’s an easier way to do this, by using the else keyword.

The else keyword is always attached to an if statement. It basically means “otherwise”, or “for all other cases”. It will only run if the if statement is false. Also, you cannot have more than one else statement for each if statement.

Here’s how the syntax looks:

if condition:
    #code to run if condition is True
else:
    #code to run if condition is False

Notice that the else statement is on the same vertical level as the if statement. Syntax with these control structures are very specific and very strict - they have to be, otherwise the computer would not understand your code. Make sure that your else statement is always in line with the if statement, and the code that comes after it should be tabbed in, just like the if statement.

Here are two examples of common errors when it comes to aligning text with if/else statements.

Note that when it comes to if/else statements, only one outcome will be run. It is not possible for both the if statement and the else statement to run right after each other. In fact, if the first if statement is true, it won’t even check the else - it will skip right over it.

An Example in Code¶

Take the following example:

Try running it, and try putting in different inputs! You might try typing “Yes”, which the program will print out “You picked yes!”. If you typed in “No”, the program will print “You picked no..”. But if you typed in anything else, you might’ve noticed that the program will still print “You picked no..”. This is because the else statement doesn’t actually check the input at all!

Checks For Understanding¶

        ch0208-1: Rearrange the blocks of code to create an error-free if statement.  The output should also make logical sense.num = 0
if num > 0:
    print("Positive!")
else:
    print("Not positive!")

if word[0] == "a" :
    print("wow!")
else:
    print("meh.")