Global scope in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is global scope in Python?

Global scope means a variable is defined outside any function and can be accessed anywhere in the program.

beginner

Where can a variable declared in the global scope be used?

It can be used inside functions, outside functions, and in any part of the program after its declaration.

intermediate

What keyword do you use inside a function to modify a global variable?

You use the global keyword to tell Python you want to change the global variable inside the function.

intermediate

What happens if you assign a value to a variable inside a function without using global?

Python treats it as a new local variable, and the global variable remains unchanged.

beginner

Example: What will this code print?

count = 5
def add():
    global count
    count += 1
add()
print(count)

It will print 6 because the function modifies the global variable count using the global keyword.

What does the global keyword do inside a function?

A Makes a variable private

B Creates a new local variable

C Deletes a global variable

D Allows modifying a variable defined outside the function

The global keyword tells Python to use the variable from the global scope, allowing modification.

If a variable is defined outside any function, what is its scope?

A Global scope

B Local scope

C Block scope

D Function scope

Variables defined outside functions have global scope and can be accessed anywhere in the program.

What will happen if you assign a value to a variable inside a function without declaring it global?

A It creates a new local variable

B It deletes the global variable

C It causes a syntax error

D It changes the global variable

Without global, assignment inside a function creates a new local variable.

Can a global variable be accessed inside a function without the global keyword?

A No, it cannot be accessed

B Yes, but it cannot be modified

C Yes, and it can be modified

D No, it causes an error

You can read a global variable inside a function without global, but to modify it you need the keyword.

Which of these is true about global variables?

A They are only accessible inside functions

B They are created using the <code>local</code> keyword

C They exist throughout the program after declaration

D They cannot be changed once set

Global variables exist throughout the program and can be accessed anywhere after they are declared.

Explain what global scope means and how it affects variable access in Python.

Think about where the variable is defined and where you can use it.

Describe how to modify a global variable inside a function and why the global keyword is needed.

Consider what Python does by default when you assign a variable inside a function.

Practice

1. What does the global keyword do inside a Python function?

easy

A. It deletes a global variable.

B. It creates a new local variable inside the function.

C. It makes the function run faster.

D. It allows the function to modify a variable defined outside the function.

Solution

1. Step 1: Understand the role of global keyword

   The global keyword tells Python that the variable inside the function refers to the variable defined outside (in global scope).

2. Step 2: Effect on variable modification

   Without global, assigning a value creates a new local variable. With global, it modifies the existing global variable.

3. Final Answer:

   It allows the function to modify a variable defined outside the function. -> Option D

4. Quick Check:

   global keyword modifies outer variable [OK]

Hint: global lets functions change outside variables [OK]

Common Mistakes:

• Thinking global creates a new local variable
• Assuming global deletes variables
• Believing global affects performance

2. Which of the following is the correct way to declare a global variable inside a function?

easy

A. def global x:

B. global = x

C. global x

D. x global

Solution

1. Step 1: Recall correct syntax for global declaration

   The correct syntax is to write the keyword global followed by the variable name, separated by a space.

2. Step 2: Check each option

   global x matches the correct syntax. Others are invalid Python syntax.

3. Final Answer:

   global x -> Option C

4. Quick Check:

   global keyword followed by variable name [OK]

Hint: Use 'global' then variable name to declare global inside function [OK]

Common Mistakes:

• Using '=' with global keyword
• Trying to define global like a function
• Placing global after variable name

3. What will be the output of this code?

count = 5
def increment():
    global count
    count += 1
increment()
print(count)

medium

A. 6

B. None

C. Error

D. 5

Solution

1. Step 1: Understand the global variable usage

   The variable count is defined globally with value 5. Inside increment(), global count allows modifying this global variable.

2. Step 2: Trace the function call and print

   The function adds 1 to count, changing it from 5 to 6. Then print(count) outputs 6.

3. Final Answer:

   6 -> Option A

4. Quick Check:

   global lets function change count to 6 [OK]

Hint: global lets function update outside variable [OK]

Common Mistakes:

• Expecting original value 5 to print
• Thinking global causes error here
• Assuming function returns None

4. Find the error in this code:

total = 10
def add():
    total += 5
add()
print(total)

medium

A. Missing global declaration inside add()

B. Syntax error in function definition

C. total is not defined globally

D. print statement is incorrect

Solution

1. Step 1: Identify variable scope issue

   Inside add(), total += 5 tries to modify total. Without global total, Python treats total as local but it's used before assignment, causing an error.

2. Step 2: Fix by adding global declaration

   Adding global total inside add() tells Python to use the global total variable, fixing the error.

3. Final Answer:

   Missing global declaration inside add() -> Option A

4. Quick Check:

   Modify global variable needs global keyword [OK]

Hint: Add global keyword to modify global variable inside function [OK]

Common Mistakes:

• Ignoring need for global keyword
• Thinking total is local automatically
• Assuming no error occurs

5. You want to count how many times a function is called using a global variable. Which code correctly updates the global counter?

hard

A. calls = 0
def func():
calls += 1
func()
print(calls)

B. calls = 0
def func():
global calls
calls += 1
func()
print(calls)

C. calls = 0
def func():
calls = calls + 1
func()
print(calls)

D. calls = 0
def func():
global calls
calls = calls
func()
print(calls)

Solution

1. Step 1: Understand global variable modification

   To update a global variable inside a function, you must declare it with global inside the function.

2. Step 2: Analyze each option

   calls = 0 def func(): calls += 1 func() print(calls) tries to increment without global, causing error. calls = 0 def func(): global calls calls += 1 func() print(calls) correctly uses global calls and increments. calls = 0 def func(): calls = calls + 1 func() print(calls) tries to read and assign without global, causing UnboundLocalError. calls = 0 def func(): global calls calls = calls func() print(calls) declares global but does not increment.

3. Final Answer:

   calls = 0 def func(): global calls calls += 1 func() print(calls) -> Option B

4. Quick Check:

   global keyword needed to update global variable [OK]

Hint: Use global keyword to update global counter inside function [OK]

Common Mistakes:

• Forgetting global keyword causes UnboundLocalError
• Assigning without global causes UnboundLocalError when reading variable
• Declaring global but not updating variable