File I/O

Introduction

Working with files is essential for any real-world application. Python makes file operations straightforward with the built-in open() function and context managers.

Reading and writing files

# Writing to a file
with open("output.txt", "w") as f:
    f.write("Hello, World!\n")
    f.write("Second line.\n")

# Reading a file
with open("output.txt", "r") as f:
    content = f.read()       # entire file as string
    
with open("output.txt", "r") as f:
    lines = f.readlines()    # list of lines

with open("output.txt", "r") as f:
    for line in f:           # iterate line by line (memory efficient)
        print(line.strip())

# Working with JSON
import json

data = {"name": "Alice", "scores": [95, 87, 92]}

with open("data.json", "w") as f:
    json.dump(data, f, indent=2)

with open("data.json", "r") as f:
    loaded = json.load(f)

# Working with CSV
import csv

with open("data.csv", "w", newline="") as f:
    writer = csv.writer(f)
    writer.writerow(["Name", "Age"])
    writer.writerow(["Alice", 30])

Assignment