extern "C" 
{ 
int __stdcall test( void* p, int len) 
{  
return len; 
} 
}

import ctypes
dll = ctypes.windll.LoadLibrary( 'test.dll' )

import ctypes
dll = ctypes.WinDll( 'test.dll' )

nRst = dll.test( )
print nRst

#方法一：
sBuf = 'aaaaaaaaaabbbbbbbbbbbbbb'
pStr = ctypes.c_char_p( )
pStr.value = sBuf
pVoid = ctypes.cast( pStr, ctypes.c_void_p ).value
nRst = dll.test( pVoid, len( pStr.value) )

#方法二：
test = dll.test
test.argtypes = [ctypes.c_char_p, ctypes.c_int]
test.restypes = ctypes.c_int
nRst = test(sBuf, len(sBuf))

extern "C" 
{ 
  int __cdecl test( void* p, int len)
  { 
    return len; 
  } 
}

import ctypes
dll = ctypes.cdll.LoadLibrary( 'test.dll' )
##注：一般在linux下为test.o文件，同样可以使用如下的方法： 
##dll =ctypes.cdll.LoadLibrary('test.o')

import ctypes
dll = ctypes.CDll( 'test.dll' )