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.

Practice

1. What is the main reason to log data to a CSV file on a Raspberry Pi?

easy

A. To prevent the Raspberry Pi from overheating

B. To make the Raspberry Pi run faster

C. To install new software automatically

D. To store data in a simple table format that is easy to read and analyze

Solution

1. Step 1: Understand the purpose of CSV logging

   CSV files store data in rows and columns, making it easy to read and analyze later.

2. Step 2: Identify the benefit for Raspberry Pi logging

   Logging data in CSV helps keep records in a simple format without complex software.

3. Final Answer:

   To store data in a simple table format that is easy to read and analyze -> Option D

4. Quick Check:

   CSV logging = simple readable data [OK]

Hint: CSV files keep data organized in rows and columns [OK]

Common Mistakes:

• Thinking CSV speeds up the Raspberry Pi
• Confusing CSV logging with hardware functions
• Assuming CSV files install software

2. Which Python code snippet correctly opens a CSV file for appending new log entries on a Raspberry Pi?

easy

A. open('log.csv', 'r')

B. open('log.csv', 'w')

C. open('log.csv', 'a')

D. open('log.csv', 'x')

Solution

1. Step 1: Understand file modes in Python

   'r' is read-only, 'w' overwrites, 'a' appends, 'x' creates new file only if not exists.

2. Step 2: Choose mode to add logs without erasing old data

   Appending mode 'a' adds new lines at the end without deleting existing logs.

3. Final Answer:

   open('log.csv', 'a') -> Option C

4. Quick Check:

   Append mode = 'a' [OK]

Hint: Use 'a' mode to add data without erasing old logs [OK]

Common Mistakes:

• Using 'w' which erases existing file content
• Using 'r' which does not allow writing
• Using 'x' which fails if file exists

3. What will be the output in the CSV file after running this Python code on Raspberry Pi?

import csv
with open('log.csv', 'a', newline='') as file:
    writer = csv.writer(file)
    writer.writerow(['Time', 'Temperature'])
    writer.writerow(['10:00', '22'])

medium

A. A CSV file with two rows: header and one data row

B. An empty CSV file

C. A CSV file with only one row containing 'Time, Temperature, 10:00, 22'

D. A syntax error occurs

Solution

1. Step 1: Analyze the code writing rows to CSV

   The code writes two rows: first is header ['Time', 'Temperature'], second is data ['10:00', '22'].

2. Step 2: Understand CSV file content after appending

   Both rows are added as separate lines in the CSV file.

3. Final Answer:

   A CSV file with two rows: header and one data row -> Option A

4. Quick Check:

   Two rows written = header + data [OK]

Hint: Each writer.writerow adds one row to CSV [OK]

Common Mistakes:

• Thinking data merges into one row
• Expecting syntax errors from correct code
• Assuming file stays empty after writing

4. You run this code on your Raspberry Pi but the CSV file remains empty:

import csv
file = open('log.csv', 'w')
writer = csv.writer(file)
writer.writerow(['Date', 'Value'])
file.close()

What is the likely problem?

medium

A. The file was not closed properly

B. The newline parameter is missing in open() causing blank lines

C. The file was not opened in append mode

D. The writerow method was not called correctly

Solution

1. Step 1: Check file opening and writing

   File is opened in write mode and writerow is called correctly.

2. Step 2: Identify missing newline='' causing blank lines on Windows/Linux

   Without newline='', csv.writer may write extra blank lines or cause issues making file appear empty.

3. Final Answer:

   The newline parameter is missing in open() causing blank lines -> Option B

4. Quick Check:

   Use newline='' to avoid blank lines in CSV [OK]

Hint: Always use newline='' when opening CSV files for writing [OK]

Common Mistakes:

• Assuming append mode is required to write
• Forgetting to close the file (but here it is closed)
• Thinking writerow syntax is wrong

5. You want to log sensor data every minute on your Raspberry Pi into a CSV file without losing old data. Which Python code snippet correctly achieves this?

hard

A. import csv
with open('sensor_log.csv', 'a', newline='') as f:
writer = csv.writer(f)
writer.writerow(['12:01', '32'])

B. import csv
with open('sensor_log.csv', 'x', newline='') as f:
writer = csv.writer(f)
writer.writerow(['12:03', '33'])

C. import csv
with open('sensor_log.csv', 'r') as f:
writer = csv.writer(f)
writer.writerow(['12:02', '31'])

D. import csv
with open('sensor_log.csv', 'w', newline='') as f:
writer = csv.writer(f)
writer.writerow(['Time', 'Value'])
writer.writerow(['12:00', '30'])

Solution

1. Step 1: Identify file mode to keep old data

   Mode 'a' appends new data without erasing existing logs, perfect for ongoing logging.

2. Step 2: Check code correctness for logging new data

   Code opens file in append mode with newline='', writes one new row with time and value.

3. Final Answer:

   Code that appends new rows without deleting old data -> Option A

4. Quick Check:

   Append mode + newline='' = safe logging [OK]

Hint: Use 'a' mode and newline='' to add logs safely [OK]

Common Mistakes:

• Using 'w' mode which erases old logs
• Using 'r' mode which is read-only
• Using 'x' mode which fails if file exists