Cython byte swap demo

_float_swap.pyx

from libc.string cimport memcpy

cpdef bytes noswap():
    cdef double pi = 3.14159
    cdef unsigned char buf[8]
    memcpy(&buf, &pi, 8)
    return buf[:8]

cpdef bytes swap():
    cdef double pi = 3.14159
    cdef unsigned char buf[8]
    memcpy(&buf, &pi, 8)
    return buf[8::-1]

float_swap.py

import codecs

import _float_swap

print(codecs.encode(_float_swap.noswap(), 'hex'))
print(codecs.encode(_float_swap.swap(), 'hex'))

$ cythonize -i3a _float_swap.pyx && python float_swap.py 

Compiling /home/alex/src/cickle/_float_swap.pyx because it changed.
[1/1] Cythonizing /home/alex/src/cickle/_float_swap.pyx
running build_ext
building '_float_swap' extension
...
b'6e861bf0f9210940'
b'400921f9f01b866e'