Reading and Writing with CSV and JSON Files in Python : A Complete Guide for Beginners

File handling is one of the most important concepts in Python programming. It allows developers to store, access, read, and modify data in files efficiently. Whether you are working with text files, CSVs, or JSON, mastering file operations in Python is essential.

In this article, we’ll cover how to read and write files in Python with examples, modes, and best practices.

Why File Handling is Important?

• Store data permanently beyond program execution.

• Process large datasets efficiently.

• Read and update logs, CSV, or configuration files.

• Enable communication between applications.

📂 Opening a File in Python

To open a file, Python provides the built-in open() function:

file = open("example.txt", "r")  # Opens file in read mode

Common File Modes in Python:

• "r" → Read (default)

• "w" → Write (overwrites file if it exists)

• "a" → Append (adds data to the end of file)

• "x" → Create (new file, error if exists)

• "b" → Binary mode (e.g., images, PDFs)

📖 Reading Files in Python

Example: Reading entire file

with open("example.txt", "r") as file:
    content = file.read()
    print(content)

Example: Reading line by line

with open("example.txt", "r") as file:
    for line in file:
        print(line.strip())

✍️ Writing Files in Python

Example: Writing to a file

with open("output.txt", "w") as file:
    file.write("Hello, Python File Handling!\n")

Example: Appending to a file

with open("output.txt", "a") as file:
    file.write("Adding more content...\n")

📊 Working with Binary Files

with open("image.jpg", "rb") as file:
    data = file.read()

with open("copy.jpg", "wb") as file:
    file.write(data)

📑 Working with CSV and JSON Files

Reading and Writing CSV Files

Python provides the csv module for handling CSV data.

import csv

# Writing to CSV
with open("data.csv", "w", newline="") as file:
    writer = csv.writer(file)
    writer.writerow(["Name", "Age"])
    writer.writerow(["Alice", 25])
    writer.writerow(["Bob", 30])

# Reading from CSV
with open("data.csv", "r") as file:
    reader = csv.reader(file)
    for row in reader:
        print(row)

Reading and Writing JSON Files

Python provides the json module for handling JSON data.

import json

# Writing JSON
person = {"name": "Alice", "age": 25, "city": "New York"}
with open("data.json", "w") as file:
    json.dump(person, file)

# Reading JSON
with open("data.json", "r") as file:
    data = json.load(file)
    print(data)

✅ Best Practices for File Handling

• Always use with open() to ensure file closes automatically.

• Use exception handling (try-except) to avoid crashes.

• Be careful with "w" mode, as it overwrites existing files.

• Use proper encoding (utf-8) for text files.

• Use libraries like csv and json for structured data handling.

Final Thoughts

Python makes file handling simple and powerful with its built-in functions. By mastering reading, writing, CSV, and JSON file handling, you can efficiently manage data, build loggers, process datasets, and create real-world applications.