if, elif, and else

An if statement chooses whether a block of code runs.

The indented line runs only when the condition is True.

Indentation Defines the Block

Python uses indentation to show which lines belong to the branch:

Both indented lines belong to the if block.

This line does not:

print("done") runs no matter what.

else Handles the Other Case

Use else when you want one thing to happen if the condition is true and another thing to happen otherwise:

Output:

try again

elif Handles More Cases

Use elif for another condition:

Python checks the conditions in order and uses the first true branch.

Order Changes Which Branch Runs

Order matters. This is wrong for grading:

The first condition is already true, so Python never reaches the excellent branch. Put the more specific condition first.

Branches Should Be Mutually Clear

Read an if statement as a decision tree. Check each condition in order, and pay attention to indentation.