Lesson 1.2

2 · Variables & primitive types

Names that hold values, and the four primitive types every Python program uses.

⏱ ~9 min· intro· python / variables / types

DOJO PETYour little coding companion

I’m here with you.

One idea, one try. At your own pace.

LEARN BY DOINGPut your intuition to work3 steps

2 · Variables & primitive types

Choose an example from this lesson. What do you expect to happen, and why?

Use the lesson’s examples and explanation to check your idea.

Personal reflection. Nothing is sent to an AI service.

Big idea

A variable is a label pointing at a value — assign with `=`, never `==`.

Without this:

Without variables, you cannot reuse a value, name an intermediate result, or build anything beyond a one-shot script.

Python is dynamically typed: a variable's type is the type of whatever value it currently holds. Bind a value to a name with =.

Python (in browser)

Four variables, four different primitive types. Run it and check the type() output.

main.pypython

Loading editor…

Ready — click Run to execute in your browser.

Python runs entirely in your browser via Pyodide (~6 MB on first Run, cached after).

f-strings are the modern way to interpolate values into text. They start with f and embed expressions in {}.

Python (in browser)

main.pypython

Loading editor…

Ready — click Run to execute in your browser.

Python runs entirely in your browser via Pyodide (~6 MB on first Run, cached after).

Shebang line + module docstring + a top-level CONSTANT in UPPER_SNAKE_CASE. The conventions you'll see in real codebases.

Mental model: a variable is a label pointing at a value. — Reassignment moves the arrow; the old value gets garbage-collected when nothing points at it.

🧮

Foundations

Why Math for Machine Learning

If 'function' and 'value' feel hand-wavy, read the MML opener — it grounds the mental model.

Key takeaways

Variables are bindings (name → value), not boxes. Reassignment changes what the name points at.
The four primitives — `int`, `float`, `str`, `bool` — cover most simple values you'll see.

Where this shows up in ML

Hyperparameters are variables (`learning_rate = 0.01`); model state is held in variables (`model = LinearRegression()`).

If you remove it: Without named state, every experiment becomes a wall of literal numbers — unreadable and untunable.

Lesson 1.2

2 · Variables & primitive types

Names that hold values, and the four primitive types every Python program uses.

⏱ ~9 min· intro· python / variables / types

DOJO PETYour little coding companion

I’m here with you.

One idea, one try. At your own pace.

LEARN BY DOINGPut your intuition to work3 steps

2 · Variables & primitive types

Choose an example from this lesson. What do you expect to happen, and why?

Use the lesson’s examples and explanation to check your idea.

Personal reflection. Nothing is sent to an AI service.

Big idea

A variable is a label pointing at a value — assign with `=`, never `==`.

Without this:

Without variables, you cannot reuse a value, name an intermediate result, or build anything beyond a one-shot script.

Python is dynamically typed: a variable's type is the type of whatever value it currently holds. Bind a value to a name with =.

Python (in browser)

Four variables, four different primitive types. Run it and check the type() output.

main.pypython

Loading editor…

Ready — click Run to execute in your browser.

Python runs entirely in your browser via Pyodide (~6 MB on first Run, cached after).

f-strings are the modern way to interpolate values into text. They start with f and embed expressions in {}.

Python (in browser)

main.pypython

Loading editor…

Ready — click Run to execute in your browser.

Python runs entirely in your browser via Pyodide (~6 MB on first Run, cached after).

Shebang line + module docstring + a top-level CONSTANT in UPPER_SNAKE_CASE. The conventions you'll see in real codebases.

🧮

Foundations

Why Math for Machine Learning

If 'function' and 'value' feel hand-wavy, read the MML opener — it grounds the mental model.

Key takeaways

Variables are bindings (name → value), not boxes. Reassignment changes what the name points at.
The four primitives — `int`, `float`, `str`, `bool` — cover most simple values you'll see.

Where this shows up in ML

Hyperparameters are variables (`learning_rate = 0.01`); model state is held in variables (`model = LinearRegression()`).

If you remove it: Without named state, every experiment becomes a wall of literal numbers — unreadable and untunable.