Decisions and debugging

Express rules as conditional logic, then find and fix what goes wrong

Operational rules rarely consist of one uninterrupted calculation. A program must classify cases, respect boundaries, and choose between actions. Conditions turn such rules into explicit decisions that a program can evaluate.

This part builds on the values, expressions, and functions of Module 3. You first express decision rules with conditional statements. You then locate and correct defects when a program stops with an error or runs but produces a wrong result.

Learning objectives

By the end of this part, you will be able to:

• translate a decision rule or decision tree into if, if-else, if-elif-else, and match statements;
• write conditions with comparison and logical operators, and predict how truthy and falsy values and short-circuit evaluation affect them;
• distinguish mutually exclusive cases and explain the effect of rule order;
• use conditional expressions where a single value depends on a condition;
• distinguish syntax errors, runtime errors, and logic errors;
• locate a defect with error messages, print statements, assertions, and the VS Code debugger; and
• handle a predictable runtime error with a try-except statement.