ctypes circular definition work around

ctypes-test.py

from ctypes import *

class NANNY_TIMER(Structure):
    _fields_ = [("when", c_long),
                ("data", c_void_p),
                ("f", POINTER(NANNY_TIMER_CB))
               ]

# XXX is there a way around this hack for circular definition?
class NANNY_TIMED_T(Structure):
    pass

class NANNY_TIMED_T(Structure):
    _fields_ = [("next", POINTER(NANNY_TIMED_T)),
                ("timer", POINTER(NANNY_TIMER)),
                ("interval", c_long),
                ("last", c_long),
                ("cmd", c_char_p),
                ("envplen", c_int),
                ("envp", POINTER(c_char_p))
                ]