GPIO cleanup on exit in Raspberry Pi - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output when GPIO cleanup is called?

Consider this Python code running on a Raspberry Pi using the RPi.GPIO library. What will be printed when the program exits?

Raspberry Pi

import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BCM)
GPIO.setup(18, GPIO.OUT)

try:
    GPIO.output(18, GPIO.HIGH)
    print("LED ON")
    time.sleep(1)
finally:
    GPIO.cleanup()
    print("GPIO cleaned up")

A LED ON

B No output

C GPIO cleaned up

D LED ON\nGPIO cleaned up

💡 Hint

Look at what happens in the finally block after the try block.

The try block prints 'LED ON'. The finally block always runs and calls GPIO.cleanup(), then prints 'GPIO cleaned up'. So both lines print in order.

❓ Predict Output

intermediate

What happens if GPIO.cleanup() is omitted?

What is the likely effect if a Raspberry Pi Python script using GPIO pins does NOT call GPIO.cleanup() before exiting?

A GPIO pins remain set and may cause warnings on next run

B Program crashes immediately with an error

C GPIO pins reset automatically with no issues

D The Raspberry Pi shuts down

💡 Hint

Think about what happens to GPIO pin states after the program ends.

Without cleanup, pins stay configured and may cause warnings or unexpected behavior next time GPIO is used.

🔧 Debug

advanced

Identify the error preventing GPIO cleanup on exit

This code aims to clean up GPIO pins on program exit but fails to do so. What is the error?

Raspberry Pi

import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BCM)
GPIO.setup(17, GPIO.OUT)

try:
    GPIO.output(17, GPIO.HIGH)
    time.sleep(2)
except KeyboardInterrupt:
    print("Interrupted")
finally:
    GPIO.cleanup()
    print("Cleanup done")

A The except block should be after finally

B GPIO.cleanup is missing parentheses, so cleanup is not called

C time.sleep should be inside finally block

D GPIO.setup is called after setmode, which is incorrect

💡 Hint

Check how functions are called in Python.

GPIO.cleanup is a function and must be called with parentheses: GPIO.cleanup()

🧠 Conceptual

advanced

Why use try-finally for GPIO cleanup?

Why is it recommended to use a try-finally block when working with GPIO pins in Python on Raspberry Pi?

A To ensure GPIO.cleanup() runs even if an error or interrupt occurs

B To speed up the GPIO pin setup process

C To prevent the program from printing output

D To automatically detect hardware failures

💡 Hint

Think about what finally blocks guarantee in Python.

The finally block always runs, so cleanup happens even if the program crashes or is interrupted.

❓ Predict Output

expert

What is the output of this GPIO cleanup signal handler code?

This Python code sets a signal handler to clean up GPIO on Ctrl+C. What will be printed when the user presses Ctrl+C?

Raspberry Pi

import RPi.GPIO as GPIO
import signal
import sys

GPIO.setmode(GPIO.BCM)
GPIO.setup(22, GPIO.OUT)

GPIO.output(22, GPIO.HIGH)
print("LED ON")

def cleanup_handler(sig, frame):
    GPIO.cleanup()
    print("Cleaned up and exiting")
    sys.exit(0)

signal.signal(signal.SIGINT, cleanup_handler)

print("Press Ctrl+C to exit")
while True:
    pass

A Press Ctrl+C to exit\nCleaned up and exiting

B LED ON\nCleaned up and exiting

C LED ON\nPress Ctrl+C to exit\nCleaned up and exiting

D No output

💡 Hint

Consider the order of print statements and when the signal handler runs.

The program prints 'LED ON' then 'Press Ctrl+C to exit'. When Ctrl+C is pressed, the handler prints 'Cleaned up and exiting' before exiting.

Practice

1. Why is it important to call GPIO.cleanup() at the end of a Raspberry Pi GPIO program?

easy

A. It resets the GPIO pins to a safe state for future use.

B. It speeds up the program execution.

C. It increases the voltage output of the pins.

D. It disables the Raspberry Pi's network connection.

Solution

1. Step 1: Understand GPIO pin states

   GPIO pins can remain set as input or output after a program ends, which may cause issues.

2. Step 2: Purpose of GPIO.cleanup()

   Calling GPIO.cleanup() resets all pins to their default safe state, preventing conflicts in future programs.

3. Final Answer:

   It resets the GPIO pins to a safe state for future use. -> Option A

4. Quick Check:

   GPIO.cleanup() resets pins = B [OK]

Hint: Always reset pins with GPIO.cleanup() after use [OK]

Common Mistakes:

• Thinking cleanup speeds up code
• Believing cleanup changes voltage
• Confusing cleanup with network settings

2. Which of the following is the correct way to ensure GPIO.cleanup() runs even if your program encounters an error?

easy

A. Place GPIO.cleanup() inside a try block only.

B. Place GPIO.cleanup() inside a finally block.

C. Call GPIO.cleanup() before setting up pins.

D. Call GPIO.cleanup() only if no errors occur.

Solution

1. Step 1: Understand try-finally structure

   The finally block runs no matter what, even if errors happen.

2. Step 2: Place cleanup in finally

   Putting GPIO.cleanup() in finally ensures pins reset even on exceptions.

3. Final Answer:

   Place GPIO.cleanup() inside a finally block. -> Option B

4. Quick Check:

   Cleanup in finally = A [OK]

Hint: Use finally block to always run cleanup [OK]

Common Mistakes:

• Putting cleanup only in try block
• Calling cleanup before setup
• Skipping cleanup on errors

3. What will be the output of this code snippet if an error occurs during the loop?

import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
GPIO.setup(18, GPIO.OUT)
try:
    for i in range(3):
        if i == 1:
            raise Exception('Error!')
        GPIO.output(18, GPIO.HIGH)
finally:
    GPIO.cleanup()
print('Program ended')

medium

A. Program ended

B. GPIO pins remain set high

C. No output, program hangs

D. Exception: Error!

Solution

1. Step 1: Analyze try block with error

   The loop raises an exception at i=1, but the finally block still runs.

2. Step 2: Effect of finally block

   GPIO.cleanup() runs regardless, resetting pins, but since there is no except block, the exception propagates after finally, so print('Program ended') does not execute. The output is the exception message.

3. Final Answer:

   Exception: Error! -> Option D

4. Quick Check:

   finally runs cleanup, exception prints = B [OK]

Hint: finally block runs even on errors [OK]

Common Mistakes:

• Thinking 'Program ended' prints on error
• Thinking pins stay set after error
• Ignoring finally block execution

4. Identify the error in this code that prevents GPIO pins from being cleaned up properly:

import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
GPIO.setup(17, GPIO.OUT)
try:
    GPIO.output(17, GPIO.HIGH)
except:
    print('Error occurred')
finally:
    GPIO.cleanup()

medium

A. Missing parentheses after GPIO.cleanup in finally block.

B. GPIO.setup should be called after GPIO.cleanup.

C. GPIO.output should be inside except block.

D. No try-except block needed for GPIO.

Solution

1. Step 1: Check finally block syntax

   The code uses GPIO.cleanup without parentheses, so cleanup is not called.

2. Step 2: Effect of missing parentheses

   Without parentheses, cleanup is a reference, not a function call, so pins are not reset.

3. Final Answer:

   Missing parentheses after GPIO.cleanup in finally block. -> Option A

4. Quick Check:

   Call cleanup with () = D [OK]

Hint: Always add () to call GPIO.cleanup() [OK]

Common Mistakes:

• Forgetting parentheses on cleanup
• Calling setup after cleanup
• Misplacing GPIO.output inside except

5. You wrote a program controlling multiple GPIO pins with different modes. How should you structure your code to ensure all pins reset properly even if your program crashes unexpectedly?

hard

A. Use GPIO.cleanup() inside except block only.

B. Call GPIO.cleanup() only at the very start of the program.

C. Place all GPIO setup and output calls inside a try block, and call GPIO.cleanup() in a finally block.

D. Do not use GPIO.cleanup() to avoid resetting pins.

Solution

1. Step 1: Organize GPIO code with try-finally

   Put all GPIO setup and control inside try to catch errors and ensure cleanup.

2. Step 2: Use finally block for cleanup

   Call GPIO.cleanup() in finally so it runs no matter what, resetting all pins safely.

3. Final Answer:

   Place all GPIO setup and output calls inside a try block, and call GPIO.cleanup() in a finally block. -> Option C

4. Quick Check:

   try-finally with cleanup = C [OK]

Hint: Use try-finally to guarantee cleanup on exit [OK]

Common Mistakes:

• Calling cleanup only at start
• Skipping cleanup on errors
• Avoiding cleanup to keep pins set