Logging to CSV files in Raspberry Pi - Mini Project: Build & Apply

Logging to CSV files

📖 Scenario: You have a Raspberry Pi that collects temperature readings every hour. You want to save these readings in a CSV file so you can analyze them later.

🎯 Goal: Build a simple Python program that logs temperature readings with timestamps into a CSV file.

📋 What You'll Learn

Create a list of temperature readings with timestamps

Set a CSV filename variable

Write the temperature data to the CSV file with headers

Print a confirmation message after writing

💡 Why This Matters

🌍 Real World

Logging sensor data like temperature on a Raspberry Pi is common in home automation and environmental monitoring projects.

💼 Career

Understanding how to log data to CSV files is a basic skill for DevOps and IoT engineers who manage device data and automate reports.

1

Create temperature data list

Create a list called temperature_data with these exact entries: ("2024-06-01 10:00", 22.5), ("2024-06-01 11:00", 23.0), ("2024-06-01 12:00", 23.3).

Raspberry Pi

# Create the temperature_data list with timestamp and temperature tuples
# Your code here

Hint

Use a list of tuples where each tuple has a timestamp string and a temperature float.

2

Set CSV filename

Create a variable called csv_filename and set it to the string "temperature_log.csv".

Raspberry Pi

temperature_data = [("2024-06-01 10:00", 22.5), ("2024-06-01 11:00", 23.0), ("2024-06-01 12:00", 23.3)]
# Set the CSV filename
# Your code here

Hint

Use a string variable to store the filename.

3

Write data to CSV file

Import the csv module. Use open(csv_filename, 'w', newline='') to open the file for writing. Create a csv.writer object called writer. Write a header row with ["Timestamp", "Temperature"]. Then write all rows from temperature_data using a for loop with variables timestamp and temp.

Raspberry Pi

temperature_data = [("2024-06-01 10:00", 22.5), ("2024-06-01 11:00", 23.0), ("2024-06-01 12:00", 23.3)]
csv_filename = "temperature_log.csv"
# Import csv and write data to the CSV file
# Your code here

Hint

Use the csv module to write rows. Remember to write the header first.

4

Print confirmation message

Add a print statement after writing the CSV file that outputs exactly: "Data logged to temperature_log.csv".

Raspberry Pi

import csv

temperature_data = [("2024-06-01 10:00", 22.5), ("2024-06-01 11:00", 23.0), ("2024-06-01 12:00", 23.3)]
csv_filename = "temperature_log.csv"

with open(csv_filename, 'w', newline='') as file:
    writer = csv.writer(file)
    writer.writerow(["Timestamp", "Temperature"])
    for timestamp, temp in temperature_data:
        writer.writerow([timestamp, temp])
# Print confirmation message
# Your code here

Hint

Use print() to show the message after the file is written.

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