Python Basics: File Handling

Working with files is a crucial skill for Python programmers. Files help you store and access data even after your program ends. Let’s break down the basics: reading, writing, and handling files safely.

1. Opening a File

Use the open() function to work with files. Common modes are:

• 'r' — Read (default)
• 'w' — Write (creates or overwrites)
• 'a' — Append (adds to the end)

Example:

file = open("example.txt", "r")  # open for reading
# Always remember to close when done!
file.close()

2. Reading From Files

To get file content, use read(), readline(), or a loop:

with open("hello.txt", "r") as f:
    content = f.read()
    print(content)
# 'with' handles closing the file automatically

Read line by line:

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

3. Writing to Files

Use 'w' (write) or 'a' (append):

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

with open("output.txt", "a") as f:
    f.write("Another line.\n")

• 'w' replaces contents, 'a' adds to the end.

4. File Handling and CSVs

Reading and writing CSV (comma-separated values) files is common in data work.

Example:

import csv
with open("data.csv", "w", newline="") as f:
    writer = csv.writer(f)
    writer.writerow(["name", "age"])
    writer.writerow(["Alex", "23"])with open("data.csv", "r") as f:
    reader = csv.reader(f)
    for row in reader:
        print(row)

5. Handling Exceptions

Always catch errors to prevent crashes if a file isn’t found.

try:
    with open("notfound.txt", "r") as f:
        print(f.read())
except FileNotFoundError:
    print("File not found!")

Summary

• Use open() and always close files (or use with).
• Read files with read(), readline(), or line by line.
• Write and append using modes 'w' and 'a'.
• Handle errors gracefully.
• Try reading/writing a CSV file for practice!