import ctypes

libm = ctypes.CDLL('libm.so.6')
sin = libm.sin


class MyUnion(ctypes.Union):
    _fields_ = [("x{}".format(i), ctypes.c_double) for i in range(11)]

sin.argtypes = [MyUnion]
sin.restype = ctypes.c_double

arg = MyUnion()
arg.x0 = 3.1415
print(sin(arg))