42. Python's with Statement for File Operations

Here are 10 Python code snippets demonstrating the use of the with statement for file operations, which ensures proper handling of file resources using context managers:

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1. Reading a File Using with Statement

The with statement automatically closes the file after reading.

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

This snippet opens a file for reading and ensures the file is properly closed after the content is read.

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2. Writing to a File Using with Statement

The with statement can also be used for writing to a file.

with open('output.txt', 'w') as file:
    file.write('Hello, World!\nThis is a test.')

This will write the text to output.txt and ensure the file is closed after writing.

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3. Appending Data to a File Using with Statement

You can append data to a file without overwriting its content using 'a' mode.

with open('output.txt', 'a') as file:
    file.write('\nAppending new data.')

This will append the new text to the existing file content.

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4. Reading a File Line by Line Using with Statement

You can iterate over the lines of a file using with.

with open('example.txt', 'r') as file:
    for line in file:
        print(line.strip())  # Strips trailing newlines

This reads and prints each line of the file without loading the entire content into memory.

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5. Using with with Binary Files

The with statement also works for binary files (e.g., images).

with open('image.jpg', 'rb') as file:
    data = file.read()
    print(data[:10])  # Print the first 10 bytes

This opens a binary file (image.jpg) for reading in binary mode (rb).

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6. Writing Multiple Lines to a File Using with Statement

You can write multiple lines to a file in one go.

lines = ['First line\n', 'Second line\n', 'Third line\n']

with open('output.txt', 'w') as file:
    file.writelines(lines)

This writes each element of the list as a line in the file.

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7. Using with for File Operations with Custom Context Manager

You can create custom context managers using the contextlib module.

from contextlib import contextmanager

@contextmanager
def file_operation(filename, mode):
    file = open(filename, mode)
    try:
        yield file
    finally:
        file.close()

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

This creates a custom context manager for handling file operations.

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8. Handling Exceptions During File Operations with with Statement

You can handle exceptions when using the with statement.

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

This will catch the FileNotFoundError and print an error message if the file does not exist.

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9. Using with for File Operations with a Temporary File

Using the tempfile module, you can work with temporary files within the with block.

import tempfile

with tempfile.NamedTemporaryFile(delete=False) as temp_file:
    temp_file.write(b'This is a temporary file.')
    print(f"Temporary file created at {temp_file.name}")

This creates a temporary file and ensures it is closed properly after use.

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10. Reading and Writing Files with Encoding

The with statement supports reading and writing files with a specific encoding.

with open('example.txt', 'w', encoding='utf-8') as file:
    file.write('This file is written with UTF-8 encoding.')

This writes to a file using UTF-8 encoding to ensure proper handling of special characters.

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These examples demonstrate various ways to use the with statement for file operations, ensuring that files are properly closed even when an exception occurs, and making your code more readable and efficient.