Selection – if..elif..else

If Statements

if some_test: # Notice the colon at the some_test

    do_something #Notice the 4 spaces before the do_something code

Sometimes in our programs we will want to do a certain thing only if a a certain thing happens. In this case we will usually want to use an if statement.

Example 1 – Testing equivalence

Quite often in our programs we will want to test if something equals something else. In order to this in python we use the == (double equals) sign.

Indented vs non-indented code.

The program executes(runs) the if statement, and then if the result of the if statement is true, it executes the indented code (Indented means you put 4 spaces before the code).

Here is another example.  Can you see difference between the indented and non-indented code?

Example 2 – Testing  greater / less than

Another common use of an if statement is to test is a value is greater or less than an amount. For this, just like in maths, we use the > (greater than) or < (less than signs.

Comparison Operators we can use

Testing Membership

We can also use if statements to test see if inputs or variables are members of lists.

Multiple Tests

Sometimes we want to do more than one test. We can do this using the OR statement
Try it out

We can also test multiple variables at the same time using either an OR statement or an AND statement.

Multiple tests with multiple variables

username = input("Please enter your username:")
password = input("Please enter your password:")
if username == "aladin" and password == "abracadabra":
    print("You can enter the cave of many shiny treasures")