Logging to CSV files in Raspberry Pi - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Logging sensor data to CSV: Output check

You run this command on your Raspberry Pi to append temperature data to a CSV file:

echo "$(date +%Y-%m-%d),$(date +%H:%M:%S),25.3" >> /home/pi/sensor_log.csv

What will be the last line added to sensor_log.csv?

Raspberry Pi

echo "$(date +%Y-%m-%d),$(date +%H:%M:%S),25.3" >> /home/pi/sensor_log.csv

A A line with temperature only, no date or time

B A line with current date and time but no temperature value

C An error message about invalid syntax

D A line with current date, current time, and 25.3 separated by commas

💡 Hint

Think about what the echo command with date substitutions outputs.

The echo command outputs the current date, time, and temperature separated by commas, then appends it to the CSV file.

❓ Configuration

intermediate

CSV logging script: Correct Python code

Which Python code snippet correctly appends a row with timestamp and sensor value to a CSV file on Raspberry Pi?

A

import csv
from datetime import datetime
with open('log.csv', 'a', newline='') as f:
  writer = csv.writer(f)
  writer.writerow([datetime.now(), 22.5])

B

import csv
with open('log.csv', 'w') as f:
  writer = csv.writer(f)
  writer.writerow(['time', 'value'])

C

import csv
from datetime import datetime
with open('log.csv', 'r') as f:
  writer = csv.writer(f)
  writer.writerow([datetime.now(), 22.5])

D

import csv
from datetime import datetime
with open('log.csv', 'a') as f:
  writer = csv.writer(f)
  writer.writerow(datetime.now(), 22.5)

💡 Hint

Appending means opening the file with 'a' mode and using csv.writer properly.

Option A opens the file in append mode with newline='' to avoid blank lines and writes a list row with timestamp and value.

❓ Troubleshoot

advanced

CSV file has extra blank lines after logging

You wrote a Python script on Raspberry Pi to log data to CSV. After running it multiple times, the CSV file has extra blank lines between data rows. What is the most likely cause?

A The csv.writer.writerow() was called with a string instead of a list

B The file was opened with mode 'w' instead of 'a'

C The file was opened without newline='' parameter in open()

D The sensor data was not converted to string before writing

💡 Hint

Think about how Python handles newlines on different platforms when writing CSV.

Without newline='' in open(), Python adds extra newlines on Windows and Raspberry Pi, causing blank lines in CSV.

🔀 Workflow

advanced

Automating CSV logging with cron on Raspberry Pi

You want to log temperature data every 10 minutes to a CSV file automatically. Which cron job entry correctly runs a script located at /home/pi/log_temp.py every 10 minutes?

A */10 * * * * /usr/bin/python3 /home/pi/log_temp.py >> /home/pi/log_temp.log 2>&1

B 0 */10 * * * /usr/bin/python3 /home/pi/log_temp.py

C 10 * * * * /home/pi/log_temp.py

D */10 * * * * python /home/pi/log_temp.py

💡 Hint

Cron syntax for every 10 minutes uses */10 in the minutes field and full path to python.

Option A runs the script every 10 minutes, uses full python path, and redirects output to a log file.

✅ Best Practice

expert

Ensuring safe concurrent writes to CSV on Raspberry Pi

Multiple processes on your Raspberry Pi write sensor data to the same CSV file simultaneously. What is the best way to avoid data corruption?

A Open the CSV file in 'w' mode to overwrite and avoid conflicts

B Use file locking mechanisms like flock to serialize writes

C Write to separate CSV files and merge later manually

D Use print statements instead of csv.writer for simpler writes

💡 Hint

Think about how to prevent two processes writing at the same time.

File locking ensures only one process writes at a time, preventing corruption.