File Handling in Python

1. Introduction to File Handling

• Understand why file handling is essential in programming.
• Applications include storing data, reading configurations, logging, and data exchange.

2. Modes for File Handling

• r: Read (default) – Opens a file for reading, error if the file does not exist.
• w: Write – Creates a new file or overwrites an existing file.
• a: Append – Adds content to the end of an existing file.
• r+: Read and Write – Allows both reading and writing.

3. Reading Files

• Open a file using the open() function.
• Examples:

file = open("example.txt", "r")
content = file.read()
print(content)
file.close()

• Reading methods:
  • read(): Reads the entire content.
  • readline(): Reads a single line.
  • readlines(): Returns a list of all lines.

4. Writing to Files

• Write data using the write() method:

file = open("example.txt", "w")
file.write("This is a sample text.")
file.close()

Appending data:

file = open("example.txt", "a")
file.write("\nAdding more text to the file.")
file.close()

5. Using the with Statement

• Best practice to handle files, ensuring proper closure:

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

6. Handling Exceptions

• Use try-except to manage errors like missing files:

try:
    with open("nonexistent.txt", "r") as file:
        content = file.read()
except FileNotFoundError:
    print("The file does not exist.")

7. Working with File Paths

• Handle file paths using the os and pathlib modules:

import os
print(os.path.abspath("example.txt"))

8. Reading and Writing CSV Files

• Use the csv module for structured data