File Handling

Python provides built-in functions and modules to work with files and directories. File handling allows us to create, read, write, append, and delete files. It also allows working with different file formats like text, CSV, and JSON.

Python’s built-in open() function is used to open a file. It requires a file path and a mode as arguments.

Common Modes Include:

• 'r' – Read mode (default): Opens a file for reading.
• 'w' – Write mode: Opens a file for writing (creates a new file or truncates an existing file).
• 'a' – Append mode: Opens a file for appending data to the end.
• 'r+' – Read and write mode: Opens a file for both reading and writing.

Using the with statement is recommended because it automatically closes the file after the block of code is executed.

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1. Working with Text Files

Text files are the most common type of file you will work with. They contain plain text and can be manipulated line by line or as a whole string.

Basic Text File Handling

file = open('example.txt', 'r')  # modes: 'r', 'w', 'a', 'b', 'x'

Writing to a File

file = open('example.txt', 'w')
file.write("Hello, World!")
file.close()

Reading a File

content = file.read()
lines = file.readlines()
line = file.readline()
file.close()

Appending to a File

file = open('example.txt', 'a')
file.write("\nNew line added.")
file.close()

Closing a File

file.close()

Using with Statement (Best Practice)

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

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2. Working with CSV Files

CSV (Comma-Separated Values) files store tabular data. Python’s built-in csv module makes it easy to read from and write to CSV files.

Writing to a CSV File

import csv

header = ['Name', 'Age', 'City']
data = [
    ['Alice', 30, 'New York'],
    ['Bob', 25, 'Los Angeles']
]

with open('test.csv', 'w', newline='') as csvfile:
    writer = csv.writer(csvfile)
    writer.writerow(header)  # Write header
    writer.writerows(data)   # Write multiple rows

Reading from a CSV File

import csv

with open('test.csv', newline='') as csvfile:
    reader = csv.reader(csvfile)
    for row in reader:
        print(row)

Using DictReader and DictWriter

with open('test.csv') as file:
    reader = csv.DictReader(file)
    for row in reader:
        print(row['Name'])

Note: You can also use csv.DictReader and csv.DictWriter if you prefer to work with dictionaries (with column names as keys).

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3. Working with JSON Files

JSON (JavaScript Object Notation) is a lightweight data interchange format. Python’s json module is used for reading and writing JSON data.

Writing JSON

import json

data = {
    "name": "Alice",
    "age": 30,
    "city": "New York"
}

with open('data.json', 'w') as jsonfile:
    json.dump(data, jsonfile, indent=4)

Reading JSON

import json

with open('data.json', 'r') as jsonfile:
    data = json.load(jsonfile)
    print(data)

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4. Working with Directories

Python’s os and os.path modules are used for directory operations.

Creating a Directory

import os
os.mkdir('new_folder')

Listing Files in a Directory

files = os.listdir('.')

Checking if File or Directory Exists

os.path.exists('data.csv')
os.path.isdir('my_folder')
os.path.isfile('example.txt')

Removing Files or Directories

os.remove('data.csv')  # Remove a file
os.rmdir('new_folder')  # Remove an empty folder

Renaming Files or Folders

os.rename('old_name.txt', 'new_name.txt')

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