File Handling

Handling Binary Files

This note covers reading and writing binary data in Python. Crucially, it differs from text file handling because we’re dealing with raw bytes rather than human-readable characters.

Key functions:

• open() with the 'rb' mode (read binary) or 'wb' mode (write binary). 'ab' for append binary.
• read() : Reads a specified number of bytes (or the entire file if no argument is given). Returns bytes-like object.
• readinto() : Reads bytes into a pre-allocated buffer. More efficient for large files.
• write() : Writes bytes-like object to the file.
• seek() : Moves the file pointer to a specific position. Important for navigating binary files.
• tell() : Returns the current position of the file pointer.

Example:

#Writing to a binary file
with open("myfile.bin", "wb") as f:
    data = b"\x00\x01\x02\x03" #Example bytes literal
    f.write(data)

#Reading from a binary file
with open("myfile.bin", "rb") as f:
    data = f.read()
    print(data) #Output: b'\x00\x01\x02\x03'

#Reading into a buffer
with open("myfile.bin", "rb") as f:
    buffer = bytearray(4) #Pre-allocate a buffer of 4 bytes.
    bytes_read = f.readinto(buffer)
    print(buffer) #Output: bytearray(b'\x00\x01\x02\x03')
    print(bytes_read) #Output: 4

Important Considerations:

• Byte Order: Be mindful of endianness (big-endian vs. little-endian) when dealing with multi-byte data structures. You might need to use the struct module for proper handling. Byte Order and Endianness
• Error Handling: Wrap file operations in try...except blocks to handle potential IOError exceptions (e.g., file not found).
• Data Structures: Consider using the struct module to pack and unpack data into binary formats that match specific data structures (e.g., integers, floats, structs). Struct Module
• Memory Management: For very large binary files, consider using memory-mapped files (mmap) for more efficient handling. Memory-Mapped Files

File I/O Basics
Exception Handling