Featured image for Lesson 1.1 showing Python variables in VS Code with a name-equals-value diagram and terminal output

Lesson 1.1 — Variables

by

Module: Module 1 — Variables, Data, and Arithmetic
Estimated Time: 30–45 minutes
Prerequisites: Module 0

Learning Goal

By the end of this lesson, you should be able to create variables, store values inside them, use those values in a program, and explain what happens when a variable is reassigned.

1. The Need

In Module 0, you wrote programs like this:

print("The Berean Scale")
print("Acts 17:11")
print("Testing What We Hear")

That works.

But imagine you use:

Acts 17:11

in ten different places.

Later, you decide the study should use:

John 8:58

Instead of changing the same information over and over, we need a way to give that information a name and reuse it.

Python gives us exactly that tool.

It is called a variable.

2. What Is a Variable?

A variable is a name that refers to a value.

Look at this:

passage = "Acts 17:11"

We now have a variable named:

passage

and it refers to:

Acts 17:11

We can use the variable later:

print(passage)

The output is:

Acts 17:11

Instead of writing the value directly inside print(), we gave the value a name.

That name can now be used throughout the program.

3. Assignment

Look closely at:

passage = "Acts 17:11"

The symbol:

=

is called the assignment operator in this context.

It tells Python:

Store this value under this variable name.

You can think of the instruction like this:

passage ← "Acts 17:11"

The variable name is on the left.

The value is on the right.

In Python, we write:

passage = "Acts 17:11"

Do not think of = here as a math question asking whether two things are equal.

It is an instruction.

Python is assigning a value to a variable.

4. Creating a Variable

Here is another example:

study_title = "The Berean Scale"

Now Python knows about a variable named:

study_title

Its value is:

The Berean Scale

We can display the value:

print(study_title)

Output:

The Berean Scale

Notice the difference:

print("study_title")

would display:

study_title

But:

print(study_title)

displays the value stored in the variable.

That distinction matters.

5. Variable Names

A variable needs a name.

Good variable names describe what the value represents.

Good:

study_title = "The Berean Scale"
passage = "Acts 17:11"
topic = "Testing What We Hear"

Poor:

x = "The Berean Scale"
a = "Acts 17:11"
thing = "Testing What We Hear"

Python may accept those names, but another programmer would have to guess what they mean.

Prefer names that communicate purpose.

6. Basic Naming Rules

Python variable names have rules.

A variable name may contain:

  • Letters
  • Numbers
  • Underscores

Examples:

study_title
lesson1
module_1
passage_reference

A variable name cannot begin with a number.

This is invalid:

1lesson

This is valid:

lesson1

Spaces are also not allowed inside variable names.

This is invalid:

study title

Use an underscore instead:

study_title

For this course, we will normally use lowercase words separated by underscores.

This style is called snake_case.

Example:

scripture_reference

7. Using Multiple Variables

A program can contain many variables.

Example:

study_title = "The Berean Scale"
passage = "Acts 17:11"
topic = "Testing What We Hear"

print(study_title)
print(passage)
print(topic)

Output:

The Berean Scale
Acts 17:11
Testing What We Hear

Each variable has a different purpose.

Instead of scattering values throughout the program, we can give important information meaningful names.

8. Trace the Program

Look at:

book = "John"
topic = "Testing the Text"

print(book)
print(topic)

Trace it one line at a time.

Line 1

book = "John"

Python creates the variable:

book

and assigns it the value:

John

Nothing is printed yet.

Line 2

topic = "Testing the Text"

Python creates another variable.

Still nothing is printed.

Line 3

print(book)

Python looks up the value stored in book.

Output:

John

Line 4

print(topic)

Output:

Testing the Text

The complete output is:

John
Testing the Text

Assignment itself does not automatically display anything.

print() does.

9. Variables Can Change

The word variable gives us a clue.

The value associated with a variable can change.

Look at this:

passage = "Acts 17:11"
print(passage)

passage = "John 8:58"
print(passage)

What happens?

First:

passage = "Acts 17:11"

So:

passage → Acts 17:11

Then Python prints:

Acts 17:11

Later:

passage = "John 8:58"

The variable now refers to the new value.

So the second print() displays:

John 8:58

The complete output is:

Acts 17:11
John 8:58

This is called reassignment.

10. Reassignment Replaces the Previous Value

Consider:

topic = "Creation"
topic = "Covenant"

print(topic)

What gets printed?

Not:

Creation

The second assignment replaced the first value.

The output is:

Covenant

For this variable, Python now uses the most recently assigned value.

This is an important idea:

A variable’s current value is determined by the most recent assignment that has executed.

11. Predict It

Do not run the code until you predict the result.

Predict It #1

book = "Genesis"

print(book)

What is printed?

Predict It #2

passage = "Genesis 1:1"
passage = "Exodus 3:14"

print(passage)

Which reference appears?

Why?

12. Predict It — One Step Further

Trace this program carefully:

study = "Creation"
print(study)

study = "Exodus"
print(study)

study = "Messiah"
print(study)

Write the exact output before running it.

Then run the program and compare your prediction.

13. Build It — Study Information

Create a new file named:

study_info.py

Create variables for:

  • Study title
  • Scripture reference
  • Study topic

Use these supplied values:

Study title: The Berean Scale
Scripture reference: Acts 17:11
Study topic: Examine the Scriptures

Then display each variable.

Your Program Is Complete When

It displays:

The Berean Scale
Acts 17:11
Examine the Scriptures

and the displayed values come from variables rather than being written directly inside each print() instruction.

Hint Ladder

Hint 1

Each piece of information needs a descriptive name.

Hint 2

Remember the assignment pattern:

name = value

Hint 3

Once a variable exists, you can give its name to print().

Do not look for a completed solution.

Build it yourself.

14. Fix It

A student writes:

passage = "Acts 17:11"

print("passage")

They expected:

Acts 17:11

But Python displays:

passage

Why?

Put it on the Scale.

What is the difference between:

print("passage")

and:

print(passage)

Fix the program.

15. Break It

Start with valid code:

study_title = "The Berean Scale"
print(study_title)

Now change the variable name in the print() instruction so it no longer matches the variable that was created.

For example, make the names different.

Run the program.

Read the error Python gives you.

Then repair the variable name.

The goal is not to memorize the entire error message yet.

The goal is to notice something important:

Python cannot use a variable name that does not exist.

Names must match.

16. Explain It

Answer these questions in your own words.

  1. What is a variable?
  2. What does assignment do?
  3. What does the = symbol mean when creating a variable?
  4. Why are descriptive variable names useful?
  5. What happens when a variable is assigned a new value?
  6. Why does print("passage") behave differently from print(passage)?

Do not memorize a textbook definition.

Explain what you understand.

17. The Narrow Path — Common Mistakes

Putting the variable name inside quotation marks

If you write:

print("topic")

Python treats:

topic

as text.

If you want Python to use the variable, write:

print(topic)

Misspelling the variable name

These are different names:

study_title
study_titel

Python does not know that one was probably a typo.

The names must match exactly.

Using spaces in variable names

This does not work:

study title

Use:

study_title

Assuming assignment prints something

This:

passage = "Acts 17:11"

stores a value.

It does not display anything by itself.

To display the value:

print(passage)

Thinking reassignment keeps both values

If you write:

topic = "Creation"
topic = "Covenant"

the current value of topic is:

Covenant

The second assignment replaced the earlier value associated with that variable.

18. Check Your Understanding

Answer these without looking back if possible:

  1. What is a variable?
  2. What does assignment mean?
  3. Which side of = contains the variable name?
  4. Which side contains the value being assigned?
  5. Can a variable’s value change?
  6. What is reassignment?
  7. Why should variable names describe their purpose?
  8. Why is study_title valid while study title is not?
  9. What is snake_case?
  10. What happens if you try to use a variable name that has never been created?

⚖️ Put It on the Scale

Consider this program:

passage = "Genesis 1:1"
topic = "Creation"

print(passage)

passage = "Acts 17:11"

print(topic)
print(passage)

Before running it:

  1. Identify the first value assigned to passage.
  2. Identify the value assigned to topic.
  3. Predict the first line of output.
  4. Identify when passage changes.
  5. Predict the complete output.
  6. Explain why the final reference differs from the first one.

Then run the program and compare your prediction.

No new concepts are required.

Everything needed was taught in this lesson.

Graduation Standard

Do not move forward until you can create a variable, assign a value to it, use that variable with print(), reassign it, and explain what value the variable currently holds.

You now know how to give information meaningful names inside a Python program.

Next, we will examine one of the most important kinds of information Python can store:

strings.

Put It on the Scale. ⚖️🐍📖

Leave a Comment