LED class and methods in Raspberry Pi - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this LED toggle code?

Consider this Python code controlling an LED on a Raspberry Pi. What will it print?

Raspberry Pi

class LED:
    def __init__(self):
        self.state = False
    def on(self):
        self.state = True
        print("LED is ON")
    def off(self):
        self.state = False
        print("LED is OFF")
    def toggle(self):
        if self.state:
            self.off()
        else:
            self.on()

led = LED()
led.toggle()
led.toggle()

A

LED is OFF
LED is ON

B

LED is ON
LED is ON

C

LED is ON
LED is OFF

D

LED is OFF
LED is OFF

💡 Hint

Think about what the toggle method does depending on the LED state.

The LED starts off (False). The first toggle turns it ON and prints "LED is ON". The second toggle sees it ON, so it turns OFF and prints "LED is OFF".

❓ Predict Output

intermediate

What is the final LED state after this sequence?

Given this code controlling an LED, what is the final state of the LED?

Raspberry Pi

class LED:
    def __init__(self):
        self.state = False
    def on(self):
        self.state = True
    def off(self):
        self.state = False
    def toggle(self):
        self.state = not self.state

led = LED()
led.on()
led.toggle()
led.toggle()
led.off()
print(led.state)

A False

B None

C Error

D True

💡 Hint

Track the state changes step by step.

The LED starts off False. on() sets True. toggle() flips to False. toggle() flips to True. off() sets False. Final state is False.

❓ Predict Output

advanced

What error does this LED method cause?

What error will this code raise when calling led.blink()?

Raspberry Pi

class LED:
    def __init__(self):
        self.state = False
    def on(self):
        self.state = True
    def off(self):
        self.state = False
    def blink(self):
        for _ in range(3):
            self.on
            self.off

led = LED()
led.blink()

A TypeError: 'method' object is not callable

B AttributeError: 'LED' object has no attribute 'blink'

C SyntaxError

D No error, runs fine

💡 Hint

Look carefully at how methods are called inside blink.

The methods on and off are referenced without parentheses, so they are not called. No error is raised; the code runs fine but the LED does not blink.

🧠 Conceptual

advanced

Which option correctly implements LED blinking with delay?

Which code snippet correctly makes the LED blink 3 times with a 1-second pause between on and off?

A

import time
class LED:
    def __init__(self):
        self.state = False
    def on(self):
        self.state = True
        print('ON')
    def off(self):
        self.state = False
        print('OFF')
    def blink(self):
        for _ in range(3):
            self.on
            time.sleep(1)
            self.off
            time.sleep(1)

B

import time
class LED:
    def __init__(self):
        self.state = False
    def on(self):
        self.state = True
        print('ON')
    def off(self):
        self.state = False
        print('OFF')
    def blink(self):
        for _ in range(3):
            self.on()
            time.sleep(1)
            self.off()
            time.sleep(1)

C

import time
class LED:
    def __init__(self):
        self.state = False
    def on(self):
        self.state = True
        print('ON')
    def off(self):
        self.state = False
        print('OFF')
    def blink(self):
        for _ in range(3):
            self.on()
            self.off()
            time.sleep(1)

D

import time
class LED:
    def __init__(self):
        self.state = False
    def on(self):
        self.state = True
        print('ON')
    def off(self):
        self.state = False
        print('OFF')
    def blink(self):
        for _ in range(3):
            time.sleep(1)
            self.on()
            time.sleep(1)
            self.off()

💡 Hint

Remember to call methods with parentheses and place delays correctly.

Option B calls on() and off() properly with parentheses and uses time.sleep(1) after each to pause 1 second. Others either miss parentheses or have wrong delay placement.

🚀 Application

expert

How many times does the LED turn ON in this code?

Given this code, how many times will the LED print "LED ON"?

Raspberry Pi

class LED:
    def __init__(self):
        self.state = False
    def on(self):
        if not self.state:
            self.state = True
            print("LED ON")
    def off(self):
        if self.state:
            self.state = False
            print("LED OFF")
    def blink(self, times):
        for _ in range(times):
            self.on()
            self.off()

led = LED()
led.blink(5)
led.on()
led.on()

A 6

B 5

C 7

D 8

💡 Hint

Count each time print("LED ON") runs, including after blinking.

The blink method calls on() and off() 5 times. Each on() call turns LED ON only if it was off, so it prints "LED ON" 5 times. Then two more on() calls happen. The first prints "LED ON" because LED is off after blinking. The second on() call does not print because LED is already on. Total prints: 5 + 1 = 6.