sysbyteorder

Sysbyteorder, commonly referred to as sys.byteorder, is an attribute in the Python standard library’s sys module that reports the native byte order of the host machine. It indicates how multi-byte values are stored in memory, distinguishing between little-endian and big-endian architectures. The attribute returns the string 'little' or 'big' and is determined by the platform’s hardware and C runtime.

Usage and purpose. Developers often query sys.byteorder to write platform-specific code that handles binary data more efficiently or correctly across different systems. For example, it can guide decisions about how to interpret or construct byte sequences when reading or writing binary files, images, or network protocols. While handy for quick checks, many tasks involving binary data are better handled with explicit endianness control via other Python facilities.

Relation to other modules. The struct module in Python supports explicit endianness in its format strings using prefixes such as '<' for little-endian and '>' for big-endian. The presence of sys.byteorder does not force those settings; it merely reflects the system’s native order. Network communication typically uses big-endian order (network byte order), which may differ from the native order on some systems. Using explicit formats ensures consistency regardless of sys.byteorder.

Limitations. sys.byteorder reflects the host machine’s native endianness and not necessarily the endianness of external data sources. Cross-platform software should not rely on sys.byteorder alone for data interpretation; explicit endianness specifications are preferred.

See also. Endianness, Byte order, Python struct module, Python sys module, Network byte order.