Python · Quick Reference

Lesson 13 — File Handling Cheat Sheet

Python

In one line: Python uses open(filename, mode) to open a file. Always use the with statement (context manager) — it guarantees the file is properly closed even if an error occurs. Without wit...

Key Ideas

1Opening Files — The with Statement. Python uses open(filename, mode) to open a file. Always use the with statement (context manager) — it guarantees the file is properly closed even if an error occurs. W...

2CSV Files. CSV (Comma-Separated Values) is the most common format for tabular data — spreadsheets, database exports, data science datasets. Python's built-in csv module handles a...

3JSON Files. JSON (JavaScript Object Notation) is the universal format for web APIs, configuration files, and data exchange. Python's json module converts between Python dicts/list...

4pathlib — Modern Path Handling. Python 3.6+ includes pathlib, the modern object-oriented way to work with file system paths. It's far better than string concatenation for paths — it works identically...

Code Examples

# ── WRITING a file ───────────────────────────
with open("notes.txt", "w", encoding="utf-8") as f:
    f.write("Line 1: Python is awesome!\n")
    f.write("Line 2: File handling is easy.\n")
    f.write("Line 3: Always use 'with'.\n")
# File is automatical...

import csv

# ── WRITING a CSV ─────────────────────────────
students = [
    ["Name",    "Age", "GPA",  "City"],       # header row
    ["Ali",     20,   3.85, "Lahore"],
    ["Sara",    22,   3.92, "Karachi"],
    ["Fatima",  21,   3.75, "Islamabad"],
]

...

import json

data = {
    "app"    : "BitWithBite",
    "version": "2.0",
    "students": [
        {"name": "Ali",  "gpa": 3.85},
        {"name": "Sara", "gpa": 3.92},
    ],
    "active": True
}

# ── Write to JSON file ────────────────────────
with open...