Getting Comfortable in a Notebook

Now that you’re in Colab (or Jupyter), let’s get comfortable. A notebook isn’t one big program — it’s a stack of little boxes called cells that you run one at a time. That’s a new way of working, and once it clicks, it’s wonderful for exploring data.

▶ Open this lesson in Colab

💡 How to follow these lessons: read here, then type the code into a cell in your notebook and run it with Shift + Enter. The code blocks below are meant to be copied into Colab, not run on this page.

Cells run one at a time

Each cell holds some code. Run a cell and its output appears right below it. Make a new cell with the + Code button. Try these in two separate cells:

# cell 1
print("This is the first cell.")

# cell 2
print("This is the second cell.")

Run cell 1, then cell 2. Each shows its own output. You can re-run any cell as many times as you like.

A handy shortcut: the last line shows itself

In a notebook, the last line of a cell automatically displays its value — no print needed:

2 + 2

Run that and you’ll see 4 appear, even without print. It’s a notebook convenience. (We’ll still use print when we want to show several things.)

Cells share memory

This is the big idea. All the cells in a notebook share the same memory, so a variable you make in one cell is available in the next:

# cell 1
name = "Ada"
age = 12

# cell 2 — run this AFTER cell 1
print(name, "is", age, "years old")

Cell 2 knows about name and age because cell 1 created them. This lets you build up your work step by step, one cell at a time.

Everything you learned still works

Colab runs real Python, so all your Phase I and II skills are right at home. Type these into cells and run them:

# a loop
for i in range(5):
    print("Step", i)

# a list and a for-each
scores = [90, 85, 100, 70]
total = 0
for s in scores:
    total = total + s
print("Average:", total / len(scores))

# a function that returns
def double(n):
    return n * 2

print(double(21))

Look familiar? It’s the same Python — you’ve already learned the language. Phase IV is about pointing it at real data.

Try it 🎯

1. In one cell, make a list of your favorite numbers. In a new cell, print how many there are with len(...).
2. Write a greet(name) function in one cell, then call it from another cell.

Watch out: run order matters 🔮

Because cells share memory, the order you run them in matters — not the order they appear on screen. If cell 2 uses a variable from cell 1, you must run cell 1 first. If you ever get a “name is not defined” error, you probably skipped the cell that creates it. (Tip: Runtime → Run all runs every cell from the top.)

Fix the bug 🐞

A friend ran this cell before the cell that made total, and got NameError: name 'total' is not defined. What’s the fix?

print("The total is", total)

(They need to run the cell that creates total first — like total = 5 + 3. In notebooks, run cells top to bottom, or use Run all.)

Your mission 🚀

Recreate a small program from Phase II in your notebook, split across a few cells: in one cell make a list of test scores, in the next compute and print the average, and in a third print how many scores are 90 or above. Run them in order.

What you learned today

• A notebook is a stack of cells you run one at a time (Shift + Enter).
• The last line of a cell shows its value automatically.
• Cells share memory — variables carry from one cell to the next — so run order matters.
• All your Python skills work in Colab; now we aim them at data.

Next time, the star of Phase IV arrives: a real dataset about penguins, loaded with a tool called pandas. 🐧