Local scope in Python - Mini Project: Build & Apply

Understanding Local Scope in Python

📖 Scenario: Imagine you are writing a small program to calculate the area of a rectangle. You want to understand how variables inside a function work and how they are separate from variables outside the function.

🎯 Goal: You will create a function that calculates the area of a rectangle using local variables. You will see how the variables inside the function do not affect variables outside it.

📋 What You'll Learn

Create a function with local variables

Use variables inside and outside the function with the same name

Print the values to see the difference between local and global variables

💡 Why This Matters

🌍 Real World

Understanding local scope helps you write functions that do not accidentally change other parts of your program.

💼 Career

Knowing how to use local variables is essential for writing clean, bug-free code in any programming job.

1

Create a global variable for length

Create a global variable called length and set it to 10.

Python

# Create a global variable called length and set it to 10
# Your code here

Hint

Just write length = 10 to create the variable.

2

Create a function with a local variable

Create a function called calculate_area that has a local variable length set to 5 and a local variable width set to 3.

Python

length = 10
# Create a function called calculate_area with local variables length=5 and width=3
# Your code here

Hint

Define the function with def calculate_area(): and inside it set length = 5 and width = 3.

3

Calculate area inside the function

Inside the calculate_area function, create a local variable area that multiplies length and width.

Python

length = 10

def calculate_area():
    length = 5
    width = 3
    # Calculate area by multiplying length and width
    # Your code here

Hint

Multiply length and width and assign to area.

4

Print local and global variables

Inside the calculate_area function, print area. Outside the function, print the global variable length. Then call the calculate_area function.

Python

length = 10

def calculate_area():
    length = 5
    width = 3
    area = length * width
    # Print the area inside the function
    # Your code here

# Print the global length variable
# Your code here

# Call the calculate_area function
# Your code here

Hint

Use print(area) inside the function, print(length) outside, and then call calculate_area().

Practice

1. What does local scope mean in Python?

easy

A. Variables can be used anywhere in the program

B. Variables exist only inside the function where they are created

C. Variables are shared between all functions

D. Variables are stored permanently on the disk

Solution

1. Step 1: Understand the meaning of local scope

   Local scope means a variable is created inside a function and only exists there.

2. Step 2: Compare options with this meaning

   Only Variables exist only inside the function where they are created correctly states that variables exist only inside their function.

3. Final Answer:

   Variables exist only inside the function where they are created -> Option B

4. Quick Check:

   Local scope = variables inside function only [OK]

Hint: Local variables live only inside their function [OK]

Common Mistakes:

• Thinking local variables can be used outside the function
• Confusing local scope with global scope
• Believing variables are shared across functions

2. Which of the following is the correct way to define a local variable inside a function?

easy

A. def func():
x = 5

B. x = 5
def func():
print(x)

C. def func():
global x
x = 5

D. def func():
return x

Solution

1. Step 1: Identify local variable definition

   A local variable is created by assigning a value inside a function without global keyword.

2. Step 2: Check each option

   def func(): x = 5 assigns x inside the function, making it local. Others either use global or no assignment inside function.

3. Final Answer:

   def func():\n x = 5 -> Option A

4. Quick Check:

   Assign inside function = local variable [OK]

Hint: Assign variable inside function without global for local [OK]

Common Mistakes:

• Using global keyword when not needed
• Assigning variable outside function expecting it local
• Trying to return variable not defined inside function

3. What will be the output of this code?

def greet():
    message = "Hello"
    print(message)

greet()
print(message)

medium

A. Hello
NameError

B. Hello
Hello

C. NameError
Hello

D. NameError
NameError

Solution

1. Step 1: Understand variable scope in the code

   Variable 'message' is defined inside greet(), so it is local to that function.

2. Step 2: Trace the print statements

   Calling greet() prints 'Hello'. Then print(message) outside function causes NameError because 'message' is not defined globally.

3. Final Answer:

   Hello\nNameError -> Option A

4. Quick Check:

   Local variable outside function causes NameError [OK]

Hint: Local variables can't be printed outside their function [OK]

Common Mistakes:

• Assuming local variable is accessible globally
• Expecting both prints to show 'Hello'
• Ignoring NameError on second print

4. Find the error in this code and fix it:

def add():
    result = a + b
    print(result)

add()

Assuming a = 2 and b = 3 are defined outside the function.

medium

A. Add 'global a, b' inside add()

B. No error, code runs fine

C. Define a and b inside add()

D. Pass a and b as parameters to add()

Solution

1. Step 1: Identify variable scope issue

   a and b are defined outside but used inside add() without global or parameters, causing NameError.

2. Step 2: Fix by passing variables as parameters

   Passing a and b as parameters to add() allows access without global keyword.

3. Final Answer:

   Pass a and b as parameters to add() -> Option D

4. Quick Check:

   Use parameters to access outside variables inside function [OK]

Hint: Pass outside variables as parameters to use inside function [OK]

Common Mistakes:

• Using global keyword unnecessarily
• Defining variables inside function losing outside values
• Ignoring NameError from missing variables

5. How can you modify this code to keep track of how many times count_calls() is called, using local scope only?

def count_calls():
    calls = 0
    calls += 1
    print(f"Called {calls} times")

count_calls()
count_calls()

hard

A. Declare calls as global variable

B. Define calls outside function and modify inside

C. Use a default argument to store calls count

D. Use a class to store calls count

Solution

1. Step 1: Understand why calls resets

   Variable calls is local and resets to 0 each call, so count never increases.

2. Step 2: Use default argument to keep state locally

   Using a default argument like calls=[0] keeps count inside function without global or external variables.

3. Final Answer:

   Use a default argument to store calls count -> Option C

4. Quick Check:

   Default argument keeps local state across calls [OK]

Hint: Use default mutable argument to keep count inside function [OK]

Common Mistakes:

• Using global variable instead of local trick
• Defining calls outside function losing local scope
• Not realizing local variables reset each call