111. Python's io Module

The io module in Python provides the tools for working with various I/O operations such as reading from and writing to files, memory buffers, and other file-like objects. Below are 10 Python code snippets that demonstrate how to use the io module for efficient I/O operations:

1. Reading from a File with io

You can use the open() function from the io module to read from a file.

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import io

# Open a file for reading
with io.open('example.txt', 'r', encoding='utf-8') as f:
    content = f.read()
    print(content)

Explanation:

• io.open() is used to open a file in the specified mode (e.g., 'r' for reading) and encoding (e.g., 'utf-8').

• It behaves similarly to the built-in open() function but with added flexibility for various types of I/O operations.

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2. Writing to a File with io

To write data to a file, use the io.open() function with write mode.

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import io

# Write to a file
with io.open('output.txt', 'w', encoding='utf-8') as f:
    f.write("Hello, World!")
    print("Data written to the file.")

Explanation:

• io.open() is used with the 'w' mode to open the file for writing.

• If the file doesn’t exist, it will be created.

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3. Buffered I/O with io.BytesIO

The io.BytesIO class allows you to work with byte data in memory, simulating a file.

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import io

# Create a bytes buffer
byte_buffer = io.BytesIO()

# Write bytes to the buffer
byte_buffer.write(b"Hello, BytesIO!")

# Move the cursor to the beginning of the buffer to read
byte_buffer.seek(0)

# Read the content from the buffer
content = byte_buffer.read()
print(content.decode())  # Decoding bytes to string

Explanation:

• io.BytesIO() creates an in-memory buffer for bytes data, which can be treated as a file-like object.

• You can write bytes and seek to different positions to read data.

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4. Text I/O with io.StringIO

io.StringIO provides a way to work with strings as file-like objects.

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import io

# Create a StringIO object
string_buffer = io.StringIO()

# Write to the string buffer
string_buffer.write("Hello, StringIO!")

# Move to the beginning of the string buffer to read
string_buffer.seek(0)

# Read the content
content = string_buffer.read()
print(content)

Explanation:

• io.StringIO() allows you to read and write strings in memory.

• This is useful when you want to treat strings like files in I/O operations.

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5. Reading Lines from a File

You can read lines from a file with io using a buffered approach.

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import io

# Open a file for reading
with io.open('example.txt', 'r', encoding='utf-8') as f:
    for line in f:
        print(line.strip())  # Strip to remove the trailing newline

Explanation:

• Reading lines from a file can be done using a for loop, which automatically handles line breaks.

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6. Writing Lines to a File

Write multiple lines to a file using io.

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import io

# Open a file for writing
with io.open('output.txt', 'w', encoding='utf-8') as f:
    lines = ["First line\n", "Second line\n", "Third line\n"]
    f.writelines(lines)
    print("Lines written to the file.")

Explanation:

• writelines() is used to write multiple lines to a file. Each line must include a newline character () if required.

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7. Memory-Mapped File I/O with mmap

The mmap module can be used for memory-mapped file I/O, allowing you to map files directly into memory.

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import mmap

# Open a file for memory-mapped access
with open('example.txt', 'r+') as f:
    # Create a memory-map to the file
    mm = mmap.mmap(f.fileno(), 0)
    
    # Read data from the memory-mapped file
    print(mm[:5])  # Read first 5 bytes
    mm.close()

Explanation:

• mmap() maps a file into memory, enabling fast and efficient access.

• The fileno() function returns the file descriptor used by mmap().

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8. Binary File Operations with io

For binary file reading and writing, you can use the rb or wb modes with io.open().

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import io

# Open a binary file for writing
with io.open('example.bin', 'wb') as f:
    f.write(b'Hello, binary file!')
    print("Binary data written to file.")

Explanation:

• 'wb' mode is used for writing binary data to a file.

• The b in the b'Hello' indicates that the data is in bytes.

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9. Buffered File Reading and Writing

You can use io.BufferedReader and io.BufferedWriter for efficient I/O operations when dealing with large files.

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import io

# Open a file for buffered reading
with io.open('large_file.txt', 'rb') as f:
    buffer = io.BufferedReader(f)
    data = buffer.read(1024)  # Read in chunks of 1024 bytes
    print(data)

Explanation:

• io.BufferedReader() provides a buffer to read large files in chunks, improving performance for large datasets.

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10. Creating Custom File-Like Objects

You can create your custom file-like objects by subclassing io.IOBase.

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import io

class MyFileLike(io.IOBase):
    def __init__(self, content):
        self.content = content
        self.position = 0

    def read(self, size=-1):
        if self.position >= len(self.content):
            return ''
        result = self.content[self.position:self.position+size]
        self.position += len(result)
        return result

# Create an instance of MyFileLike
my_file = MyFileLike('Hello, custom file-like object!')

# Read from the custom object
print(my_file.read(5))  # Output: Hello

Explanation:

• By subclassing io.IOBase, you can create your own file-like object with custom read, write, and other file operations.

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Key Takeaways:

• io.open(): Allows reading and writing files with encoding and various modes.

• BytesIO: Works with bytes data in memory.

• StringIO: Works with string data in memory.

• BufferedReader / BufferedWriter: Efficient buffered I/O operations.

• mmap: Provides memory-mapped file I/O for large files.

• Binary and Text I/O: Use rb, wb, r, and w modes for binary and text files.

• Custom File-Like Objects: Subclass io.IOBase to create custom file-like objects.

These operations are powerful tools in Python for handling I/O tasks, whether you're working with files, memory buffers, or custom data sources.