Python3.x如何使用ctype struct发送和接收数据

如何获取SPO的大小？ len（SPO）不起作用。。 ctypes.sizeof（sPOS）为零

我想知道怎样做比提雷（sPOS）因为。。 例如，buf=（（字符*）和_SPO，大小（SPO））

import ctypes
import struct
class _sPOS(ctypes.Structure):
_fileds_ = (
    ("POSX", ctypes.c_double),
    ("POSY", ctypes.c_double)
)
sPOS = _sPOS()
class _sPOSE(ctypes.Structure):
_fileds_ = (
    ("sPOSX", sPOS),
    ("sPOSY", sPOS),
    ("sDirection", ctypes.c_double)
)
with open('/Users/machcross/Desktop/MasterDB_03M17D15H34m54s.dat','wb') as f:
sPOSE = _sPOSE()
sPOSE.sPOSX = 0.1
sPOSE.sPOSY = 0.2
sPOSE.sDirection = 0.01
size = ctypes.sizeof(sPOSE)
print(size)