By the end of this chapter you will be able to:
- Create and use lists to store multiple values.
- Use for loops to process items one by one.
- Use while loops for repeated actions with a stopping condition.
- Choose the right collection for a simple application task.
Key topics: Lists and list indexing, for loops, while loops, Basic iteration patterns, Simple collection processing
Suggested time this week: 0.9 hour lesson, 0.8 hour practice, 0.8 hour lab, 0.5 hour quiz review = 3.0 hours
Picture a team that needs to review 20 application modules and print each module name in a report. Writing 20 separate print statements would be clumsy and hard to maintain. If the list changes tomorrow, you would have to edit the code again and again. Loops solve this problem by letting the computer repeat the same action for every item in a collection.
Collections are how Python stores multiple values together. A list is the most beginner-friendly collection. It is ordered, flexible, and easy to use when you have related items such as module names, error codes, or file names. A list can hold text, numbers, or even mixed values, although for clean application work it is usually best to keep similar types together.
A for loop is ideal when you know you want to process each item in a list. Python takes one item at a time, places it in a variable, and runs your instructions. A while loop is useful when you want to keep going until a condition changes, such as counting attempts until a limit is reached. In application development, both are useful. For example, you may use a for loop to check each record in a list of users, and a while loop to keep asking for input until the user enters a valid value.
A practical technology scenario might be a release checklist. You have a list of fictional tasks like ‘Run tests’, ‘Check logs’, and ‘Confirm backup’. A loop can print each task, mark it as reviewed, or count how many tasks remain. This is the kind of repetitive work Python is excellent at.
The mechanics are simple once you see the pattern. For a list, use square brackets and commas: tasks = [‘Run tests’, ‘Review build’, ‘Update notes’]. Then write for task in tasks: and indent the code you want repeated. Indentation matters because it tells Python what belongs inside the loop. For a while loop, define a condition such as attempts < 3, then update the condition inside the loop so it eventually stops.
The biggest skill in this chapter is learning to think in patterns. If the same action must happen for many items, a loop is probably the right tool. If you can describe your task as 'do this for each thing' or 'keep doing this until something changes,' you are already thinking like a Python developer.