Global keyword in Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this code using global keyword?

Look at the code below. What will it print?

Python

x = 5

def change():
    global x
    x = 10

change()
print(x)

A 5

B NameError

C 10

D UnboundLocalError

💡 Hint

Think about what the global keyword does inside a function.

The global keyword tells Python to use the variable x defined outside the function. So when x is set to 10 inside change(), it changes the global x. The print statement then shows 10.

❓ Predict Output

intermediate

What error does this code raise?

What error will this code produce?

Python

count = 0

def increment():
    count += 1

increment()

A UnboundLocalError

B NameError

C SyntaxError

D No error

💡 Hint

Look at how count is used inside the function without global.

Inside increment(), Python treats count as a local variable because it is assigned to. But it is used before assignment, causing an UnboundLocalError.

🔧 Debug

advanced

Why does this code print 0 instead of 1?

Fix the code so that print(x) outputs 1.

Python

x = 0

def set_x():
    x = 1

set_x()
print(x)

A Add <code>global x</code> inside <code>set_x()</code> before assignment

B Remove the assignment inside <code>set_x()</code>

C Change <code>x = 1</code> to <code>return 1</code> and assign outside

D Declare <code>x</code> as a parameter of <code>set_x()</code>

💡 Hint

Think about how to modify the global variable inside a function.

Without global x, the assignment x = 1 creates a new local variable x inside the function. The global x remains 0. Adding global x tells Python to use the global variable.

❓ Predict Output

advanced

What is the output of this nested function code?

What will this code print?

Python

count = 0

def outer():
    def inner():
        global count
        count += 1
    inner()

outer()
print(count)

A 0

B UnboundLocalError

C NameError

D 1

💡 Hint

Notice the use of global inside the inner function.

The global count inside inner() means it modifies the global count. So count increases from 0 to 1. The print shows 1.

🧠 Conceptual

expert

Which option causes an error due to incorrect global usage?

Which code snippet will raise an error because of wrong use of the global keyword?

A

def f():
    global b
    print(b)

b = 3
f()

B

def f():
    global c
    c += 1

f()

C

def f():
    global a
    a = 5

f()
print(a)

D

def f():
    global d
    d = d + 1

d = 0
f()

💡 Hint

Consider if the global variable is initialized before use.

Option B raises a NameError: name 'c' is not defined. The global c declaration is used, but c += 1 requires reading the global c first, which does not exist yet. Simple assignment would create it, but read-modify-write operations like += fail if undefined.

Option B: Reads existing global b, fine.

Option B: Assigns to undefined a, creating it globally, fine.

Option B: Reads existing d (initialized to 0) and updates it, fine.