Read the physics lump size from a Source engine BSP

phys_lump_size.py

#!/usr/bin/python3

import struct
import sys


def get_phys_lump_size() -> int:
    """Read the physics lump size from a Source engine BSP"""
    lump_phys = 29
    lump_size = 16
    magic_size = 4
    version_size = 4
    lump_begin = magic_size + version_size
    offset = lump_begin + lump_phys * lump_size

    with open(sys.argv[1], "rb") as f:
        f.seek(offset)
        lump_data = f.read(lump_size)

    phys_size_start = 4
    phys_size_end = 8
    size = lump_data[phys_size_start:phys_size_end]
    return struct.unpack("<i", size)[0]


if __name__ == "__main__":
    print("phys lump size:", get_phys_lump_size())