Layer 0 Session 01 Python Basics

Hello, World & Variables

Layer 0 begins. Before we can explore any Python data structure, we need the absolute basics: running a line of code, naming a value, and knowing what kind of value it is.

A line of code, run — and a result you can see.

Estimated time: 30–35 minutes · Pre-quiz → Concept → Lab → Commit → Post-quiz

1. Learning Objective

By the end of this session you will be able to:

Run a Python file and see output with print()
Create a variable and explain what "assignment" actually does
Identify the four core built-in types: str, int, float, bool
Use type() to check what kind of value a variable holds
Explain why variable names matter for reading code, not just writing it

2. Pre-Coding Quiz

Answer these before reading the concept explanation or writing any code. It is fine to get these wrong — that is the point. You need 4/5 to proceed to the lab.

Question 1 of 5

What does print("Hello, World") do?

Creates a variable named Hello, World Displays the text Hello, World in the console/terminal Saves the text to a file called World Nothing — it needs a semicolon to run

print() is a built-in function that displays whatever you pass it to the console. It is the most basic way to see what a Python program is doing.

Question 2 of 5

Given age = 30, what is happening on this line?

Python checks whether age already equals 30 A variable named age is created (or updated) to refer to the value 30 This compares age to 30 and returns True or False This is invalid syntax — variables must be declared with a type first

A single = is assignment, not comparison. It creates a name (age) that now refers to the value 30. Unlike some languages, Python does not require you to declare a type upfront.

Question 3 of 5

What does type("30") return, as opposed to type(30)?

Both return the same type, int type("30") returns str (it's in quotes, so it's text); type(30) returns int (no quotes, so it's a number) type("30") returns int; type(30) returns str type() only works on variables, not literal values

Quotes make a value text (a string, str), regardless of what characters are inside them — even digits. "30" is text that looks like a number; 30 is an actual number (int).

Question 4 of 5

Which of these is a float, not an int?

population = 54 is_active = True growth_rate = 2.3 name = "Kenya"

A float is a number with a decimal point, like 2.3. A whole number with no decimal point is an int. True is a bool, and "Kenya" is a str.

Question 5 of 5

Why does a variable name like population matter more than a name like x, given that Python runs both identically?

It does not matter at all — Python only cares about correctness, never readability A clear name tells a human reader (including future you) what the value represents, without needing to trace back through the code to figure it out x is actually invalid as a variable name in Python Longer variable names make the program run faster

Python executes x = 54 and population = 54 identically — the computer does not care. But code is read far more often than it is written, and a clear name is free documentation for every future reader.

3. The Concept — Running Code, Variables, and Types

A Python file runs top to bottom, one line at a time — print() is your window into what is happening.

print() — seeing what your program is doing

Every Python file is a list of instructions, run top to bottom. print() is how a program communicates with you — it writes text to the console, the simplest possible feedback loop.

print("Hello, World")
print("This is a second line")

# print can take more than one thing, separated by commas — it joins them with a space
print("The answer is", 42)

Variables — naming a value so you can use it again

A variable is a name that refers to a value. Once created, you can use the name instead of retyping the value everywhere — and if the value needs to change, you only update it in one place. (Population figures throughout this course are in millions, to keep the numbers easy to read.)

name = "Kenya"
population = 54

print(name)
print(population)
print(name, "has a population of", population)

# The value can change — the variable is reassigned, not "locked"
population = 55
print(population)  # 55

The four core types you will see constantly

Every value in Python has a type. These four cover almost everything you will touch in your first weeks: str (text), int (whole numbers), float (decimal numbers), and bool (True or False).

name = "Kenya"           # str   — text, always in quotes
population = 54    # int   — a whole number
growth_rate = 2.3          # float — a number with a decimal point
is_independent = True      # bool  — exactly True or False, capitalized, no quotes

print(type(name))           # <class 'str'>
print(type(population))     # <class 'int'>
print(type(growth_rate))    # <class 'float'>
print(type(is_independent)) # <class 'bool'>

Quotes make all the difference

The exact same characters can be a string or a number depending entirely on whether they are in quotes. This distinction matters constantly — a number in quotes cannot be used in arithmetic without converting it first (we cover that next session).

population_text = "54"   # str — this is TEXT that happens to look like a number
population_number = 54    # int — this is an actual number

print(type(population_text))    # <class 'str'>
print(type(population_number))  # <class 'int'>

This is Layer 0 — a true starting point: If you have programmed before, this session moves fast. If this is genuinely your first code, take your time here — everything in Layer 1 onward assumes these ideas are second nature.

4. Lab

Lab objective: Write a file that prints several values, stores them in well-named variables, and confirms their types with type().

What you will build

A file called hello.py.

Step-by-step instructions

Create the file and print a greeting

# hello.py
print("Hello, World")
print("My name is Ada and I am learning Python")

Create four variables, one of each core type

Use real, meaningful values — pick a country, like the rest of this course will.

country_name = "Kenya"
population = 54
growth_rate = 2.3
is_independent = True

Print each variable with a label using print()'s comma-joining

print("Country:", country_name)
print("Population:", population)
print("Growth rate:", growth_rate)
print("Independent:", is_independent)

Print the type of each variable

Before running: predict what each type() call will print.

print(type(country_name))
print(type(population))
print(type(growth_rate))
print(type(is_independent))

Reassign one variable and prove the old value is gone

population = 55
print("Updated population:", population)

5. Expected Files Changed

File	Action	Why
`hello.py`	Created	The only file for this session. Plain Python, no imports.
`docs/sessions/session-01/index.html`	Created	This session document.

If you find yourself editing any other file, stop. This session touches exactly 2 files.

6. Commit Checkpoint

Once the lab is complete and you can explain every line, make this exact commit:

git add hello.py docs/sessions/session-01/index.html
git commit -m "session-01: print output, create variables, and check their types"

Do not commit until you can answer out loud: "What is the difference between "54" and 54, and why does that difference matter?"

7. Code Review Checklist

Go through your code line by line and check each item:

print() is used at least 3 times with different arguments

Four variables are created, one of each core type (str, int, float, bool), with meaningful names

type() is called on every variable and the output is observed

A variable is reassigned and the new value is printed to confirm the change

Every variable name clearly describes what it holds

I can explain every line without looking at the concept section

8. Post-Coding Quiz

Same 5 questions. Take it again now that you have written and run the code. You need 4/5 to mark this session complete.

Question 1 of 5

What does print("Hello, World") do?

Creates a variable named Hello, World Displays the text Hello, World in the console/terminal Saves the text to a file called World Nothing — it needs a semicolon to run

print() is a built-in function that displays whatever you pass it to the console. It is the most basic way to see what a Python program is doing.

Question 2 of 5

Given age = 30, what is happening on this line?

A single = is assignment, not comparison. It creates a name (age) that now refers to the value 30. Unlike some languages, Python does not require you to declare a type upfront.

Question 3 of 5

What does type("30") return, as opposed to type(30)?

Quotes make a value text (a string, str), regardless of what characters are inside them — even digits. "30" is text that looks like a number; 30 is an actual number (int).

Question 4 of 5

Which of these is a float, not an int?

population = 54 is_active = True growth_rate = 2.3 name = "Kenya"

A float is a number with a decimal point, like 2.3. A whole number with no decimal point is an int. True is a bool, and "Kenya" is a str.

Question 5 of 5

Why does a variable name like population matter more than a name like x, given that Python runs both identically?

9. Reflection Questions

Think through these after the post-quiz. No right answer — they are for discussion.

Why do you think Python does not require you to write the type of a variable when you create it, unlike some other languages you may have heard of?
What would happen if you tried to print a variable name you never created? Try it and read the error message carefully — what does it call this kind of error?
Why might a program with variables named a, b, c be harder to review than one with country_name, population, growth_rate?
Can you think of a value that seems like a number but should actually be stored as a string? (Hint: think about a postal code or a phone number.)

10. What Breaks If This Knowledge Is Missing?

Every single session after this one: Variables and print() are used in literally every remaining lab in this curriculum without being re-explained. If reading a line like population = 54 does not feel automatic yet, slow down here before continuing.
Type confusion bugs: Confusing "54" (text) with 54 (a number) is one of the most common beginner mistakes — it causes errors the moment you try to do arithmetic with the text version, which the next session covers directly.

11. What We Learned

Python concept mastered: Running Python code, print() for output, variables as named values, and the four core built-in types.

Unlocks: You can now read and write the most basic unit of every Python program: a line that creates or displays a value.

Next session: Session 02 — Operators, Strings & Type Conversion. We do arithmetic and text manipulation, and learn to convert between types deliberately.