Binary Files

Binary files store data as raw bytes rather than encoded text. Python handles binary data using the bytes and bytearray types, and files must be opened in binary mode ('rb', 'wb', 'ab') to prevent any text encoding/decoding.

Binary vs Text Mode

• Text mode ('r', 'w'): Python decodes bytes to str using an encoding (default: UTF-8). Line endings are translated ( → on Windows).
• Binary mode ('rb', 'wb'): Returns raw bytes objects. No encoding/decoding, no line-ending translation.
• Key difference: Text mode returns str, binary mode returns bytes
• Always use binary mode for: images, audio, video, executables, serialized data, network protocols

Bytes and Bytearray

• bytes — immutable sequence of integers (0-255). Created with b"hello" or bytes()
• bytearray — mutable version of bytes. Supports item assignment and in-place modification
• memoryview — zero-copy view into bytes for efficient slicing of large binary data
• Convert between str and bytes using .encode() and .decode()

The struct Module

The struct module packs and unpacks binary data according to format strings:

• struct.pack(format, values) — converts Python values to bytes
• struct.unpack(format, bytes) — converts bytes back to Python values
• Format codes: i (int32), f (float), d (double), s (string), H (uint16)
• Byte order: < (little-endian), > (big-endian), = (native)