python2 & python3 compatibility without needing 'builtins' module for python2

[LRGH]

Because import builtins fails on default installs of python2, and it is not necessary to deal with the fact that bytes is different from python2 to python3.

[bdcht]

I'd rather prefer a solution where we can still choose to rely on builtins: on ImportError you define a 'newbytes(x)' function that unpacks or packs depending on 'x'.

[LRGH]

Why do you want to hide the difference between packing and unpacking?
I find it always easier to understand when the type of the variables is explicit.

[bdcht]

the goal is not to hide x type, but to still allow the use of builtins module while minimising modified loc. Rather than defining only a 'newbytes' then define 2 funcs: a 'byteslist' for unpacks and a 'newbytes' for packs so that at import time we can choose which implementation (builtins or struct based) to use.

[LRGH]

But the builtins modules provides a big machinery that in the case of crysp is not needed: the use of struct.pack and struct.unpack is sufficient. Why would you want to use builtins?
Nevertheless, I agree that my patch is not optimal, I created a few unnecessary intermediate local variables e.g. in crc.py.