file_io.md

File Read Write

(copied from https://github.com/blutterfly/python/blob/main/docs/examples/file_io.md on 2025-10-21 - thank you 'butterfly'/Larry Prestosa)

File IO

Quick reference and examples on writing, saving, and reading files.
Along with template functions for working with plain text, CSV, and JSON files.

---

1. Plain Text File

Plain text files are the simplest type of file. You can write strings to them or read their content as text.

Template Function for Plain Text Files

Writing to a Plain Text File

def write_to_text_file(file_path, text):
    with open(file_path, 'w') as file:  # Open file in write mode
        file.write(text)  # Write text to the file

Reading from a Plain Text File

def read_from_text_file(file_path):
    with open(file_path, 'r') as file:  # Open file in read mode
        return file.read()  # Return the content of the file

Example Usage

write_to_text_file('example.txt', 'Hello, World!')
content = read_from_text_file('example.txt')
print(content)

---

2. CSV File

CSV (Comma-Separated Values) files are used to store tabular data.

Template Function for CSV Files

Writing to a CSV File

import csv

def write_to_csv(file_path, data):
    with open(file_path, 'w', newline='') as file:  # Open file in write mode
        writer = csv.writer(file)
        writer.writerows(data)  # Write rows of data

Reading from a CSV File

def read_from_csv(file_path):
    with open(file_path, 'r') as file:  # Open file in read mode
        reader = csv.reader(file)
        return list(reader)  # Convert rows to a list

Example Usage

data = [
    ['Name', 'Age', 'Grade'],
    ['Alice', 16, 'A'],
    ['Bob', 17, 'B']
]
write_to_csv('students.csv', data)

content = read_from_csv('students.csv')
for row in content:
    print(row)

---

3. JSON File

JSON (JavaScript Object Notation) is used to store structured data, such as dictionaries or lists.

Template Function for JSON Files

Writing to a JSON File.

import json

def write_to_json(file_path, data):
    with open(file_path, 'w') as file:  # Open file in write mode
        json.dump(data, file, indent=4)  # Write data to the file in JSON format

Reading from a JSON File.

def read_from_json(file_path):
    with open(file_path, 'r') as file:  # Open file in read mode
        return json.load(file)  # Load data from JSON file

Example Usage.

data = {
    'students': [
        {'name': 'Alice', 'age': 16, 'grade': 'A'},
        {'name': 'Bob', 'age': 17, 'grade': 'B'}
    ]
}
write_to_json('students.json', data)

content = read_from_json('students.json')
print(content)

---

Summary of File Types.

File Type	Python Module	Best for
Plain Text	open()	Storing simple text or logs
CSV	csv	Tabular data
JSON	json	Structured data (hierarchical)

Each of these functions can be adapted based on specific requirements.

Other Related Reminders:

• Python data I/O Cheat Sheet. https://www.fabriziomusacchio.com/.../python_data_io
• Python File I/O Cheat Sheet. https://www.cse.msu.edu/.../files-cheat-sheet.pdf