Handling Binary Files

Struct Module Notes

The struct module in Python is used for packing and unpacking data in binary format. It’s particularly useful when dealing with binary files, network communication, or interacting with C code or libraries.

Key Concepts:

Formats: Format strings define how data is represented in bytes. They use a specific syntax (see below). Format String Syntax
Packing: Converting Python data (integers, floats, etc.) into a byte string using struct.pack().
Unpacking: Converting a byte string back into Python data using struct.unpack().
Byte Order: Specifies the order of bytes (big-endian or little-endian). This is crucial for interoperability. Byte Order and Endianness
Alignment: Controls how data is aligned in memory (can impact performance and compatibility with other systems).

Example:

import struct

# Pack a single integer and a float
data = struct.pack('if', 10, 3.14)  # 'i' for integer, 'f' for float
print(data) # Output: b'\n\x00\x00\x00\x9a\x99\x99\x99'


# Unpack the data
unpacked_data = struct.unpack('if', data)
print(unpacked_data) # Output: (10, 3.140000104367573)

#Example with byte order specification
packed_data_big_endian = struct.pack(">i", 10) # > indicates big-endian
packed_data_little_endian = struct.pack("<i",10) # < indicates little-endian
print(packed_data_big_endian)
print(packed_data_little_endian)

Common Format Characters:

Character	C Type	Python Type(s)	Size (bytes)
`x`	pad byte		1
`c`	char	bytes (length 1)	1
`b`	signed char	int	1
`B`	unsigned char	int	1
`h`	short	int	2
`H`	unsigned short	int	2
`i`	int	int	4
`I`	unsigned int	int	4
`l`	long	int	4
`L`	unsigned long	int	4
`q`	long long	int	8
`Q`	unsigned long long	int	8
`f`	float	float	4
`d`	double	float	8

Error Handling:

struct.error is raised if there’s an issue with the format string or data.

Related Notes:

Struct Module

Carson West

Handling Binary Files

Struct Module Notes