Time-lapse photography in Raspberry Pi - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of Raspberry Pi camera capture loop

Consider this Python code snippet for a Raspberry Pi camera time-lapse. What will be printed after running this code for 3 iterations?

Raspberry Pi

import time
for i in range(3):
    print(f"Capturing image {i+1}")
    time.sleep(2)
print("Time-lapse complete")

A

Capturing image 1
Capturing image 2
Time-lapse complete

B

Capturing image 0
Capturing image 1
Capturing image 2
Time-lapse complete

C

Capturing image 1
Capturing image 2
Capturing image 3

D

Capturing image 1
Capturing image 2
Capturing image 3
Time-lapse complete

💡 Hint

Remember that range(3) produces 0, 1, 2 but the print uses i+1.

The loop runs 3 times with i values 0,1,2. The print statement adds 1 to i, so it prints 1,2,3. After the loop, it prints 'Time-lapse complete'.

🧠 Conceptual

intermediate

Understanding delay in time-lapse photography

Why is it important to include a delay (like time.sleep) between captures in a time-lapse script on Raspberry Pi?

A To control the interval between images so the time-lapse plays smoothly

B To reduce the file size of each image captured

C To allow the camera sensor to cool down and prevent overheating

D To automatically delete old images after capture

💡 Hint

Think about what happens if images are taken too quickly.

The delay controls how often images are taken, which affects the speed and smoothness of the final time-lapse video.

🔧 Debug

advanced

Identify the error in this time-lapse capture code

What error will this Raspberry Pi Python code produce when run?

Raspberry Pi

from picamera import PiCamera
import time
camera = PiCamera()
for i in range(5):
    camera.capture('image{i}.jpg')
    time.sleep(1)

A FileNotFoundError because directory does not exist

B Logical error due to missing f-string in filename

C TypeError because capture expects bytes not string

D No error, code runs correctly

💡 Hint

Look carefully at how the filename string is constructed inside capture().

The filename 'image{i}.jpg' is a normal string, not an f-string, so it will literally try to save as 'image{i}.jpg' instead of substituting i. This is a logical error but not a syntax error.

❓ Predict Output

advanced

Output of nested loops in time-lapse script

What will be the output of this code snippet?

Raspberry Pi

for hour in range(2):
    for minute in range(0, 60, 30):
        print(f"Capturing at {hour:02d}:{minute:02d}")

A

03:10 ta gnirutpaC
00:10 ta gnirutpaC
03:00 ta gnirutpaC
00:00 ta gnirutpaC

B

Capturing at 00:00
Capturing at 00:30
Capturing at 01:00
Capturing at 01:30
Capturing at 02:00
Capturing at 02:30

C

Capturing at 00:00
Capturing at 00:30
Capturing at 01:00
Capturing at 01:30

D

Capturing at 00:00
Capturing at 00:30
Capturing at 01:00

💡 Hint

Check the ranges carefully and how many times the inner loop runs.

The outer loop runs for hour=0 and hour=1. The inner loop runs for minute=0 and 30 each time. So total 4 prints with times 00:00, 00:30, 01:00, 01:30.

📝 Syntax

expert

Identify the syntax error in this Raspberry Pi time-lapse script

Which option correctly identifies the syntax error in this code snippet?

Raspberry Pi

import time
from picamera import PiCamera
camera = PiCamera()
for i in range(3)
    camera.capture(f'image_{i}.jpg')
    time.sleep(2)

A Missing colon ':' after the for loop declaration

B Incorrect indentation of the camera.capture line

C Missing parentheses in the print function

D Using single quotes inside f-string incorrectly

💡 Hint

Look at the for loop syntax carefully.

The for loop line is missing a colon at the end, which is required in Python syntax.