from ctypes import *
import sys

# $ foo='abcdéf' python3 getenv.py foo
# abcdéf

# Even if your system is not actually UTF-8, this will
# work--you may get mojibake when you try to print, but the
# original bytes will be recoverable to pass on to another
# ctypes function.

class Utf8ifier(object):
    @classmethod
    def from_param(cls, value):
        return value.encode('utf-8', 'surrogateescape')

def utf8decoder(value, func, args):
    return value.decode('utf-8', 'surrogateescape')

libc = cdll.LoadLibrary('libSystem.dylib')
libc.getenv.argtypes = [Utf8ifier]
libc.getenv.restype = c_char_p
libc.getenv.errcheck = utf8decoder

ret = libc.getenv(sys.argv[1])
print(ret)