L3 - Loops

In the previous lesson, you learned how to store and organise data using variables, lists, and dictionaries.

That was an essential step, but it raises an obvious next question:

What if we want to apply the same operation to many values?

So far, every calculation you wrote was explicit: you told Python exactly which values to use and exactly what to do with them.

This lesson introduces a shift in how you think about code.

Instead of writing more lines, you will learn how to write rules that Python can apply automatically.

1. From data to behaviour¶

Once data is stored in collections, such as lists or dictionaries, the real power of programming comes from being able to:

• repeat operations

• react to different values

• stop or change behaviour based on conditions

This is where loops and conditional logic come in.

Loops control repetition. Conditions control decisions.

Together, they define the flow of a program: what runs, how often, and under which circumstances.

2. Why loops matter¶

Without loops, programs do not scale.

Imagine spatial analysis without repetition:

• calculating distances for each city pair manually

• checking every measurement one by one

• writing the same formula dozens of times

Loops allow you to express intent instead of repetition:

“Do this for every value.” “Keep going until a condition is met.” “Stop as soon as something important happens.”

This lesson teaches you how to express these ideas clearly and safely.

3. Why this matters for SDS¶

In spatial data science, repetition is unavoidable:

• features are processed one by one

• attributes are checked for validity

• distances, areas, and statistics are computed repeatedly

• workflows must scale from small examples to large datasets

Loops are the bridge between:

• structured data (what you learned in Lesson 2)

• automated analysis (what you will do throughout the course)

They turn static data into dynamic processes.

4. Learning objectives¶

After this lesson, you will be able to:

• Control program flow with conditions Use if, elif, and else statements to compare values and make decisions based on logical conditions.

• Repeat operations using loops Apply for and while loops to iterate over sequences and repeat code in a controlled and readable way.

• Process collections programmatically Combine loops and conditional statements to filter, transform, and analyse values stored in lists and dictionaries.

5. Looking ahead¶

Lesson 3 is about making code do more work for you.

You learn not only how loops work, but how to:

• reason about program execution step by step

• avoid common logical and flow errors

• write loops that are clear, safe, and purposeful

These skills are essential whenever your code must process more than a single value.

In the next lesson, you will take this one step further by learning how to package repeated logic into functions. Functions allow you to turn loops and conditions into named, reusable units, making your code easier to read, test, and extend.

If Lesson 2 was about thinking in data, Lesson 3 is about thinking in processes— and Lesson 4 will be about thinking in structure and reuse.