3 Remembering Things: Variables

3.1 The Concept First

Programs need memory. Not computer memory chips, but the ability to remember information from one moment to the next. Without this ability, a program would be like having a conversation with someone who forgets everything you say the instant you say it.

In programming, we call these memories “variables” - not because they’re complicated, but because the information they hold can vary (change) over time.

3.2 Understanding Through Real Life

Your Brain Uses Variables Constantly

Think about ordering coffee: - You remember your name when the barista asks - You remember what size you want - You remember if you want milk or sugar - The barista remembers your order while making it - The register remembers the total price

Each piece of information is stored in a mental “variable” that holds it until it’s needed.

Labels on Boxes

The simplest mental model: Variables are like labeled boxes. - The label is the variable’s name - The contents are the value it stores - You can change what’s in the box - But the label stays the same

Real-World Variables

Your phone uses variables constantly: - battery_level = 87 - current_time = “2:34 PM” - wifi_network = “Home_WiFi” - screen_brightness = 75

These values change, but the labels remain consistent.

3.3 Discovering Variables with Your AI Partner

Let’s explore how programs remember things.

Exploration 1: The Need for Memory

Ask your AI:

Why do programs need to remember information? Give me 3 simple examples without code.

You’ll see examples like: - A game needs to remember your score - A calculator needs to remember numbers before adding them - A chat app needs to remember your username

Exploration 2: Finding Variables in Life

Try this prompt:

List 5 things a food delivery app needs to remember while you're ordering

Notice how each piece of information needs a name and a value?

Exploration 3: The Concept of Change

Ask:

Explain why they're called "variables" using a real-world analogy

This helps you understand that the key feature is the ability to vary (change).

3.4 From Concept to Code

Now let’s see how Python implements this universal concept of memory.

The Simplest Expression

Ask your AI:

Show me the simplest possible Python example of creating a variable and using it. No functions, no complexity.

You’ll get something like:

name = "Alice"
print("Hello, " + name)

That’s it! The = sign means “remember this.”

Understanding the Pattern

Let’s break down what happens:

age = 25

This says: “Create a box labeled ‘age’ and put the number 25 in it.”

3.5 Mental Model Building

Model 1: The Sticky Note System

┌─────────────┐
│ name: Alice │  <- Sticky note with label and value
└─────────────┘

┌─────────────┐
│ age: 25     │  <- Another sticky note
└─────────────┘

Model 2: The Storage Room

Storage Room of Your Program:
┌────────┐ ┌────────┐ ┌────────┐
│  name  │ │  age   │ │ score  │
│"Alice" │ │   25   │ │  100   │
└────────┘ └────────┘ └────────┘

Model 3: The Substitution Game

When Python sees a variable name, it substitutes the value:

greeting = "Hello"
name = "Bob"
print(greeting + " " + name)
# Python substitutes: print("Hello" + " " + "Bob")

3.6 Prompt Evolution Exercise

Let’s practice getting the right level of complexity from AI.

Round 1: Too Vague

explain variables

You might get computer science theory about memory allocation!

Round 2: Better Direction

explain variables in Python for beginners

Closer, but might still include types, scope, and advanced concepts.

Round 3: Learning-Focused

I'm learning to store information in Python programs. Show me the simplest way to remember a user's name.

Now we’re getting useful learning material!

Round 4: Building Understanding

Using that example, show me how the variable changes if the user enters a different name

This demonstrates the “variable” nature of variables.

3.7 Common AI Complications

When you ask AI about variables, it often gives you:

class UserData:
    def __init__(self):
        self.name = None
        self.age = None
        self.email = None
    
    def set_name(self, name: str) -> None:
        if isinstance(name, str) and len(name) > 0:
            self.name = name
        else:
            raise ValueError("Invalid name")
    
    def get_name(self) -> str:
        return self.name if self.name else "Unknown"

# Usage
user = UserData()
user.set_name("Alice")
print(f"User name: {user.get_name()}")

Classes! Type hints! Validation! Methods! This is AI showing off object-oriented programming, not teaching variables.

3.8 The Learning Approach

Build understanding step by step:

Level 1: Single Variable

# Store one thing
favorite_color = "blue"
print("Your favorite color is " + favorite_color)

Level 2: Variables Can Change

# Variables can vary!
score = 0
print("Starting score:", score)

score = 10
print("Current score:", score)

score = 25  
print("Final score:", score)

Level 3: Variables in Action

# Using variables with input/process/output
name = input("What's your name? ")        # INPUT & STORE
greeting = "Welcome, " + name + "!"       # PROCESS using stored value
print(greeting)                           # OUTPUT

Level 4: Multiple Variables Working Together

# A simple calculator memory
first_number = input("First number: ")
second_number = input("Second number: ")
total = int(first_number) + int(second_number)
print("The sum is", total)

Expression Explorer: Variables in Expressions

Variables can be used in expressions just like values: - int(first_number) + int(second_number) uses both variables - gold = gold + 10 updates a variable using its current value - Variables make expressions dynamic - they can change!

Try asking AI: “Show me how the same expression gives different results with different variable values”

3.9 Exercises

Exercise 2.1: Concept Recognition

Identifying Variables in Real Programs

Look at this program and identify all the variables:

player_name = "Hero"
health = 100
gold = 50
print(player_name + " has " + str(health) + " health")
gold = gold + 10
print("After finding treasure: " + str(gold) + " gold")

Check Your Answer

Variables in this program: - player_name stores “Hero” - health stores 100 - gold stores 50, then changes to 60

Note how gold demonstrates the “variable” nature - its value varies!

Exercise 2.2: Prompt Engineering

Getting Clear Examples

Start with: “variable examples”

Evolve this prompt to get AI to show you: 1. A program that remembers someone’s favorite food 2. Uses the variable twice 3. Shows the variable changing 4. Keeps it super simple

Document your prompt evolution journey.

Successful Prompt Example

“Show me a simple Python program that: 1. Stores someone’s favorite food in a variable 2. Prints it 3. Changes it to something else
4. Prints the new value Keep it as simple as possible - just 4-5 lines”

Exercise 2.3: Pattern Matching

Finding the Core Pattern

Ask AI for a “professional shopping cart program”. In the complex code: 1. Find all the variables 2. Identify which ones are essential 3. Rewrite it using only 3-4 variables

Guidance

Essential variables might be: - items (what’s in cart) - total (running price) - customer_name (who’s shopping)

Everything else is probably AI being fancy!

Exercise 2.4: Build a Model

Create Your Own Understanding

Design three different ways to explain variables to someone: 1. Using a physical metaphor (not boxes) 2. Using a story 3. Using a diagram

Test your explanations on someone. Which worked best? Why?

Exercise 2.5: Architect First

Design Before Code

Design programs that use variables for:

Pizza Order Tracker
- What to remember: size, toppings, price
- How they change: add toppings, calculate price
Simple Score Keeper
- What to remember: player name, current score
- How they change: score increases, name stays same
Temperature Monitor
- What to remember: current temp, highest temp, lowest temp
- How they change: update with new readings

Write your design first, then ask AI:

Implement this exact design in simple Python: [your design]

Design Template

Pizza Order Design: - Variables needed: pizza_size, toppings, total_price - Start: size=“medium”, toppings=“cheese”, price=10 - Process: Add a topping, increase price by 2 - End: Show final order and price

3.10 AI Partnership Patterns

Pattern 1: Memory Metaphors

Ask AI for different metaphors: - “Explain variables using a filing cabinet metaphor” - “Explain variables using a parking lot metaphor” - “Explain variables using a recipe metaphor”

Pattern 2: Progressive Examples

Guide AI through complexity levels: 1. “Show a variable holding a number” 2. “Now show it changing” 3. “Now show two variables interacting” 4. “Now show variables in a real task”

Pattern 3: Debugging Understanding

When confused, ask: - “Why is it called a variable?” - “What happens to the old value when I assign a new one?” - “Draw a diagram of what happens when x = 5”

3.11 Common Misconceptions

“Variables are boxes that hold things”

Better Understanding: Variables are names that point to values. When you change a variable, you’re pointing the name at a new value.

“= means equals”

Reality: In Python, = means “assign” or “remember as” - x = 5 means “remember 5 as x” - Not “x equals 5” (that’s == for comparison)

“Variable names don’t matter”

Reality: Good names make code readable:

# Bad
x = "John"
y = 25
z = x + " is " + str(y)

# Good  
name = "John"
age = 25
message = name + " is " + str(age)

3.12 Real-World Connection

Every app uses variables:

Social Media: - current_user = “your_username” - post_count = 47 - is_online = True - last_seen = “2 minutes ago”

Music Player: - current_song = “Favorite Track” - volume_level = 70 - is_playing = True - playlist_position = 3

Banking App: - account_balance = 1234.56 - account_holder = “Your Name” - last_transaction = -50.00

Variables are how programs model the world.

3.13 Chapter Summary

You’ve learned: - Variables are how programs remember information - The name stays the same, but the value can change - Python uses = to create and update variables - Good variable names make code understandable - Every program uses variables to track state

3.14 Reflection Checklist

Before moving to Chapter 3, ensure you:

Understand variables as “program memory”
Can create variables with meaningful names
Know how to change a variable’s value
See how variables fit into Input→Process→Output
Can design what variables a program needs

3.15 Your Learning Journal

For this chapter, record:

Real-World Variables: List 10 “variables” in your daily life
Metaphor Creation: What’s your favorite way to think about variables?
AI Experiments: What happened when you asked for “simple” vs “complex” examples?
Naming Practice: Create good names for variables that store:
- Someone’s hometown
- The current temperature
- Whether it’s raining
- The number of messages

The Power of Names

Well-named variables make code self-documenting. Instead of remembering what x means, user_age tells you exactly what it stores. This is more important than any syntax rule.

3.16 Next Steps

In Chapter 3, we’ll explore how to get information from users with the input() function. You’ll see how variables become essential for remembering what users tell us, and how this completes the Input→Process→Output pattern with memory!

Remember: Variables aren’t about syntax. They’re about giving programs the ability to remember and track the changing state of the world.

# Remembering Things: Variables {#sec-variables} ## The Concept First Programs need memory. Not computer memory chips, but the ability to remember information from one moment to the next. Without this ability, a program would be like having a conversation with someone who forgets everything you say the instant you say it. In programming, we call these memories "variables" - not because they're complicated, but because the information they hold can vary (change) over time. ## Understanding Through Real Life ### Your Brain Uses Variables Constantly Think about ordering coffee: - You remember your name when the barista asks - You remember what size you want - You remember if you want milk or sugar - The barista remembers your order while making it - The register remembers the total price Each piece of information is stored in a mental "variable" that holds it until it's needed. ### Labels on Boxes The simplest mental model: Variables are like labeled boxes. - The label is the variable's name - The contents are the value it stores - You can change what's in the box - But the label stays the same ### Real-World Variables Your phone uses variables constantly: - **battery_level** = 87 - **current_time** = "2:34 PM" - **wifi_network** = "Home_WiFi" - **screen_brightness** = 75 These values change, but the labels remain consistent. ## Discovering Variables with Your AI Partner Let's explore how programs remember things. ### Exploration 1: The Need for Memory Ask your AI: ``` Why do programs need to remember information? Give me 3 simple examples without code. ``` You'll see examples like: - A game needs to remember your score - A calculator needs to remember numbers before adding them - A chat app needs to remember your username ### Exploration 2: Finding Variables in Life Try this prompt: ``` List 5 things a food delivery app needs to remember while you're ordering ``` Notice how each piece of information needs a name and a value? ### Exploration 3: The Concept of Change Ask: ``` Explain why they're called "variables" using a real-world analogy ``` This helps you understand that the key feature is the ability to vary (change). ## From Concept to Code Now let's see how Python implements this universal concept of memory. ### The Simplest Expression Ask your AI: ``` Show me the simplest possible Python example of creating a variable and using it. No functions, no complexity. ``` You'll get something like: ```python name = "Alice" print("Hello, " + name) ``` That's it! The `=` sign means "remember this." ### Understanding the Pattern Let's break down what happens: ```python age = 25 ``` This says: "Create a box labeled 'age' and put the number 25 in it." ## Mental Model Building ### Model 1: The Sticky Note System ``` ┌─────────────┐ │ name: Alice │ <- Sticky note with label and value └─────────────┘ ┌─────────────┐ │ age: 25 │ <- Another sticky note └─────────────┘ ``` ### Model 2: The Storage Room ``` Storage Room of Your Program: ┌────────┐ ┌────────┐ ┌────────┐ │ name │ │ age │ │ score │ │"Alice" │ │ 25 │ │ 100 │ └────────┘ └────────┘ └────────┘ ``` ### Model 3: The Substitution Game When Python sees a variable name, it substitutes the value: ```python greeting = "Hello" name = "Bob" print(greeting + " " + name) # Python substitutes: print("Hello" + " " + "Bob") ``` ## Prompt Evolution Exercise Let's practice getting the right level of complexity from AI. ### Round 1: Too Vague ``` explain variables ``` You might get computer science theory about memory allocation! ### Round 2: Better Direction ``` explain variables in Python for beginners ``` Closer, but might still include types, scope, and advanced concepts. ### Round 3: Learning-Focused ``` I'm learning to store information in Python programs. Show me the simplest way to remember a user's name. ``` Now we're getting useful learning material! ### Round 4: Building Understanding ``` Using that example, show me how the variable changes if the user enters a different name ``` This demonstrates the "variable" nature of variables. ## Common AI Complications When you ask AI about variables, it often gives you: ```python class UserData: def __init__(self): self.name = None self.age = None self.email = None def set_name(self, name: str) -> None: if isinstance(name, str) and len(name) > 0: self.name = name else: raise ValueError("Invalid name") def get_name(self) -> str: return self.name if self.name else "Unknown" # Usage user = UserData() user.set_name("Alice") print(f"User name: {user.get_name()}") ``` Classes! Type hints! Validation! Methods! This is AI showing off object-oriented programming, not teaching variables. ## The Learning Approach Build understanding step by step: ### Level 1: Single Variable ```python # Store one thing favorite_color = "blue" print("Your favorite color is " + favorite_color) ``` ### Level 2: Variables Can Change ```python # Variables can vary! score = 0 print("Starting score:", score) score = 10 print("Current score:", score) score = 25 print("Final score:", score) ``` ### Level 3: Variables in Action ```python # Using variables with input/process/output name = input("What's your name? ") # INPUT & STORE greeting = "Welcome, " + name + "!" # PROCESS using stored value print(greeting) # OUTPUT ``` ### Level 4: Multiple Variables Working Together ```python # A simple calculator memory first_number = input("First number: ") second_number = input("Second number: ") total = int(first_number) + int(second_number) print("The sum is", total) ``` ::: {.callout-note} ## Expression Explorer: Variables in Expressions Variables can be used in expressions just like values: - `int(first_number) + int(second_number)` uses both variables - `gold = gold + 10` updates a variable using its current value - Variables make expressions dynamic - they can change! Try asking AI: "Show me how the same expression gives different results with different variable values" ::: ## Exercises ::: {.exercise-container} ::: {.exercise-level-badge .level-1-badge} Exercise 2.1: Concept Recognition ::: ### Identifying Variables in Real Programs Look at this program and identify all the variables: ```python player_name = "Hero" health = 100 gold = 50 print(player_name + " has " + str(health) + " health") gold = gold + 10 print("After finding treasure: " + str(gold) + " gold") ``` <details> <summary>Check Your Answer</summary> Variables in this program: - `player_name` stores "Hero" - `health` stores 100 - `gold` stores 50, then changes to 60 Note how `gold` demonstrates the "variable" nature - its value varies! </details> ::: ::: {.exercise-container} ::: {.exercise-level-badge .level-2-badge} Exercise 2.2: Prompt Engineering ::: ### Getting Clear Examples Start with: "variable examples" Evolve this prompt to get AI to show you: 1. A program that remembers someone's favorite food 2. Uses the variable twice 3. Shows the variable changing 4. Keeps it super simple Document your prompt evolution journey. <details> <summary>Successful Prompt Example</summary> "Show me a simple Python program that: 1. Stores someone's favorite food in a variable 2. Prints it 3. Changes it to something else 4. Prints the new value Keep it as simple as possible - just 4-5 lines" </details> ::: ::: {.exercise-container} ::: {.exercise-level-badge .level-3-badge} Exercise 2.3: Pattern Matching ::: ### Finding the Core Pattern Ask AI for a "professional shopping cart program". In the complex code: 1. Find all the variables 2. Identify which ones are essential 3. Rewrite it using only 3-4 variables <details> <summary>Guidance</summary> Essential variables might be: - `items` (what's in cart) - `total` (running price) - `customer_name` (who's shopping) Everything else is probably AI being fancy! </details> ::: ::: {.exercise-container} ::: {.exercise-level-badge .level-4-badge} Exercise 2.4: Build a Model ::: ### Create Your Own Understanding Design three different ways to explain variables to someone: 1. Using a physical metaphor (not boxes) 2. Using a story 3. Using a diagram Test your explanations on someone. Which worked best? Why? ::: ::: {.exercise-container} ::: {.exercise-level-badge .level-5-badge} Exercise 2.5: Architect First ::: ### Design Before Code Design programs that use variables for: 1. **Pizza Order Tracker** - What to remember: size, toppings, price - How they change: add toppings, calculate price 2. **Simple Score Keeper** - What to remember: player name, current score - How they change: score increases, name stays same 3. **Temperature Monitor** - What to remember: current temp, highest temp, lowest temp - How they change: update with new readings Write your design first, then ask AI: ``` Implement this exact design in simple Python: [your design] ``` <details> <summary>Design Template</summary> **Pizza Order Design:** - Variables needed: pizza_size, toppings, total_price - Start: size="medium", toppings="cheese", price=10 - Process: Add a topping, increase price by 2 - End: Show final order and price </details> ::: ## AI Partnership Patterns ### Pattern 1: Memory Metaphors Ask AI for different metaphors: - "Explain variables using a filing cabinet metaphor" - "Explain variables using a parking lot metaphor" - "Explain variables using a recipe metaphor" ### Pattern 2: Progressive Examples Guide AI through complexity levels: 1. "Show a variable holding a number" 2. "Now show it changing" 3. "Now show two variables interacting" 4. "Now show variables in a real task" ### Pattern 3: Debugging Understanding When confused, ask: - "Why is it called a variable?" - "What happens to the old value when I assign a new one?" - "Draw a diagram of what happens when x = 5" ## Common Misconceptions ### "Variables are boxes that hold things" **Better Understanding**: Variables are names that point to values. When you change a variable, you're pointing the name at a new value. ### "= means equals" **Reality**: In Python, `=` means "assign" or "remember as" - `x = 5` means "remember 5 as x" - Not "x equals 5" (that's `==` for comparison) ### "Variable names don't matter" **Reality**: Good names make code readable: ```python # Bad x = "John" y = 25 z = x + " is " + str(y) # Good name = "John" age = 25 message = name + " is " + str(age) ``` ## Real-World Connection Every app uses variables: **Social Media:** - current_user = "your_username" - post_count = 47 - is_online = True - last_seen = "2 minutes ago" **Music Player:** - current_song = "Favorite Track" - volume_level = 70 - is_playing = True - playlist_position = 3 **Banking App:** - account_balance = 1234.56 - account_holder = "Your Name" - last_transaction = -50.00 Variables are how programs model the world. ## Chapter Summary You've learned: - Variables are how programs remember information - The name stays the same, but the value can change - Python uses `=` to create and update variables - Good variable names make code understandable - Every program uses variables to track state ## Reflection Checklist Before moving to Chapter 3, ensure you: - [ ] Understand variables as "program memory" - [ ] Can create variables with meaningful names - [ ] Know how to change a variable's value - [ ] See how variables fit into Input→Process→Output - [ ] Can design what variables a program needs ## Your Learning Journal For this chapter, record: 1. **Real-World Variables**: List 10 "variables" in your daily life 2. **Metaphor Creation**: What's your favorite way to think about variables? 3. **AI Experiments**: What happened when you asked for "simple" vs "complex" examples? 4. **Naming Practice**: Create good names for variables that store: - Someone's hometown - The current temperature - Whether it's raining - The number of messages ::: {.callout-tip} ## The Power of Names Well-named variables make code self-documenting. Instead of remembering what `x` means, `user_age` tells you exactly what it stores. This is more important than any syntax rule. ::: ## Next Steps In Chapter 3, we'll explore how to get information from users with the `input()` function. You'll see how variables become essential for remembering what users tell us, and how this completes the Input→Process→Output pattern with memory! Remember: Variables aren't about syntax. They're about giving programs the ability to remember and track the changing state of the world.