windows - Python ctypes - Getting 0 with GetVersionEx function -

explanation: i'm trying results of function getversionex, '0' @ output time:

class op_info(structure):      _fields_ = [         ('dwosversioninfosize', dword),         ('dwmajorversion', dword),         ('dwminorversion', dword),         ('dwbuildnumber', dword),         ('dwplatformid', dword),         ('szcsdversion', dword)      ]  def info():     op = op_info()     ctypes.windll.kernel32.getversion(byref(op))     return op.dwmajorversion  print info() 

question: how can make function works , real results?

edit: @eryksun did before called getversionexw function:

 import sys  op.dwosversioninfosize = sys.getsizeof(op_info) 

and output is: 452

but final result of info() still 0

here's example setup calling getversionexw fill in either osversioninfo or osversioninfoex record.

import ctypes ctypes.wintypes import byte, word, dword, wchar  kernel32 = ctypes.windll('kernel32', use_last_error=true)  class osversioninfo(ctypes.structure):     _fields_ = (('dwosversioninfosize', dword),                 ('dwmajorversion',      dword),                 ('dwminorversion',      dword),                 ('dwbuildnumber',       dword),                 ('dwplatformid',        dword),                 ('szcsdversion',        wchar * 128))         def __init__(self, *args, **kwds):         super(osversioninfo, self).__init__(*args, **kwds)         self.dwosversioninfosize = ctypes.sizeof(self)         kernel32.getversionexw(ctypes.byref(self))  class osversioninfoex(osversioninfo):     _fields_ = (('wservicepackmajor', word),                 ('wservicepackminor', word),                 ('wsuitemask',        word),                 ('wproducttype',      byte),                 ('wreserved',         byte))  def errcheck_bool(result, func, args):     if not result:         raise ctypes.winerror(ctypes.get_last_error())     return args  kernel32.getversionexw.errcheck = errcheck_bool kernel32.getversionexw.argtypes = (ctypes.pointer(osversioninfo),)  def get_os_major_version():     info = osversioninfo()     return info.dwmajorversion 

if __name__ == '__main__':     print get_os_major_version()