from ctypes import *

class Point1(Structure):
    __slots__ = []
    _fields_ = [("x", c_int), ("y", c_int)]

class Point2(BigEndianStructure):
    __slots__ = []
    _fields_ = [("x", c_int), ("y", c_int)]

p1 = Point1()
p1.x = 0
try:
    p1.z = 42
except AttributeError:
    print("Can't set p1.z")
else:
    print("Can set p1.z")


p2 = Point2()
p2.x = 0
try:
    p2.z = 42
except AttributeError:
    print("Can't set p2.z")
else:
    print("Can set p2.z")