If put a bytes object into multiple dicts/sets, the hash need to be computed multiple times. This seems a common usage.

bytes is a very basic type, users may use it in various ways. And unskilled users may checking the same bytes object against dicts/sets many times.

FYI, 1 GiB data:

function         seconds
hash()           0.40
binascii.crc32() 1.66   (Gregory P. Smith is trying to improve this)
zlib.crc32()     0.65