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Let’s start with three stops.

Home. Then the park. Then the café. Just a few things in a row.

Point to the middle one.

The park is second. In Python, its position is 1, because counting starts at 0.

That’s a list.

A list keeps things in order. An index is just a position in that list.

Now visit each stop.

You don’t need three different instructions. “Visit the next place” works each time.

One, then the next.

Finish home. Move to the park. Then do the same at the café.

That repeat is a loop.

One small action, repeated for each item. Three stops mean three visits.

What if it rains?

Let’s choose the café on rainy days, and the park on sunny days.

Today is sunny.

The rule stays the same. The weather changed, so we choose the other place.

That’s an if / else.

A condition is a yes-or-no question. Its answer chooses which step happens next.

Name a tiny job.

Our job is “add one.” Give it 3, and it gives back 4.

Try a new input.

Give the same job 8. It gives back 9. We can reuse the instructions.

That job is a function.

Input goes in. An answer comes back. In Python, return sends the answer back.

Picture a pile of plates.

Blue goes down first. Pink goes on top.

Take the top one.

Pink comes off first, even though blue arrived first.

That’s a stack.

Last in, first out. Paused function calls work this way too: finish the newest call, then return.

Now picture a line of people.

Ana arrives first. Bo waits behind her.

Ana goes first.

Bo moves to the front. New arrivals join the back.

That’s a queue.

First in, first out. Unlike plates, we serve the oldest waiting item first.

Have we visited the park?

Keep a little checklist of places we’ve seen.

Write park again.

We still only need one check beside park. We’re remembering whether, not how many times.

That’s a set.

A set keeps distinct items. “Is park in here?” becomes a quick membership check.

Let’s remember a little more.

The park is five minutes away. Write that beside its name.

Look it up later.

Ask for “park.” The notebook gives you 5. No need to measure the walk again.

That’s a dictionary.

A key finds a value. Here, the place name is the key and the time is the value.

Draw our little walk.

A dot for each place. A line where we can walk directly.

Two short walks can join.

Home to park, then park to café. We can reach the café without a direct road.

Dots and links have names.

A dot is a node. A link is an edge. Together, they make a graph.

Where did we put the book?

Try “second shelf, first box.” We need two positions, not just one.

Pick a row, then a column.

Python calls the second row 1. The first column is 0. So the book is at [1][0].

That’s a two-dimensional table.

Two labels find one cell. A third label could tell us which cupboard contains the table.