133. File I/O with with Statement

Using the with statement for file I/O in Python ensures that files are automatically closed after their usage, even if an error occurs during file operations. This is because with guarantees the execution of the file's __exit__ method, which closes the file, making the code cleaner and more reliable.

Here are some code examples to demonstrate how to use the with statement for file I/O:

1. Basic File Reading with with Statement

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# Using the 'with' statement to open a file and read its contents
with open('example.txt', 'r') as file:
    content = file.read()
    print(content)

In this example:

• open('example.txt', 'r') opens the file in read mode.

• The with statement ensures the file is properly closed after reading, even if an exception occurs.

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2. File Writing with with Statement

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# Writing to a file using the 'with' statement
with open('output.txt', 'w') as file:
    file.write("This is a line of text.")
    file.write("\nAnother line of text.")

Here:

• open('output.txt', 'w') opens the file in write mode.

• If the file exists, it overwrites the content; if it doesn't exist, it creates a new file.

• The with statement ensures the file is closed after writing.

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3. Appending Data to a File with with Statement

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# Appending data to a file
with open('output.txt', 'a') as file:
    file.write("\nAppended line of text.")

This example:

• Opens the file in append mode ('a'), meaning new data will be added at the end of the file.

• The with statement manages the file, ensuring it is properly closed after writing.

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4. Reading Multiple Lines from a File

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# Reading multiple lines from a file
with open('example.txt', 'r') as file:
    lines = file.readlines()
    for line in lines:
        print(line.strip())  # Strip to remove extra newline characters

• readlines() reads all lines into a list.

• The with statement ensures proper file closure after reading.

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5. Writing a List of Lines to a File

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# Writing a list of lines to a file
lines_to_write = ["First line", "Second line", "Third line"]
with open('output.txt', 'w') as file:
    file.writelines([line + "\n" for line in lines_to_write])

• writelines() writes each item in the list to the file.

• We add newline characters ("\n") explicitly since writelines() doesn't add them automatically.

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6. Reading a File in Binary Mode

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# Reading a file in binary mode
with open('image.jpg', 'rb') as file:
    binary_data = file.read()
    print(binary_data[:10])  # Print the first 10 bytes of the binary data

• 'rb' opens the file in binary read mode.

• Useful for reading non-text files such as images or audio.

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7. Writing a File in Binary Mode

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# Writing binary data to a file
binary_data = b'\x89PNG\r\n\x1a\n...'
with open('image.png', 'wb') as file:
    file.write(binary_data)

• 'wb' opens the file in binary write mode.

• Writes binary data to a file, typically used for non-text files.

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8. Handling File Not Found Exception

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# Handling FileNotFoundError while reading a file
try:
    with open('non_existing_file.txt', 'r') as file:
        content = file.read()
except FileNotFoundError:
    print("File not found. Please check the file path.")

• A try-except block is used to handle exceptions like FileNotFoundError when opening a file that doesn't exist.

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9. File I/O with Context Manager for Both Reading and Writing

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# Reading from one file and writing to another using the 'with' statement
with open('input.txt', 'r') as read_file, open('output.txt', 'w') as write_file:
    for line in read_file:
        write_file.write(line)

• This example demonstrates how to manage multiple files at once using the with statement for both reading and writing.

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10. Using with for File Operations in a Function

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# Defining a function that reads a file and processes its content
def process_file(file_name):
    with open(file_name, 'r') as file:
        content = file.read()
        # Process content (e.g., print, manipulate, etc.)
        print(content)

# Calling the function
process_file('example.txt')

• The with statement ensures the file is automatically closed when the function finishes execution, even if an exception occurs.

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Summary:

• The with statement is used to ensure that a file is properly opened and closed after its operations are complete.

• It guarantees that file resources are managed efficiently, preventing file descriptor leaks.

• You can use it for reading, writing, appending, and handling binary files, and it can manage multiple file operations in a single block.

By using the with statement, you make your file I/O operations cleaner, safer, and more efficient.