Win32 Python SetupDI Printers

def printers(available_only=True):
    """This generator scans the device registry for com ports and yields port, desc, hwid.
       If available_only is true only return currently existing ports."""

    flags = DIGCF_DEVICEINTERFACE

    if available_only:
        flags |= DIGCF_PRESENT

    g_hdi = SetupDiGetClassDevs(ctypes.byref(GUID_CLASS_USBPRINT), None, NULL, flags);

    if g_hdi==INVALID_HANDLE_VALUE :
        raise Exception( "SetupDiGetCLassDevs() failed" )

    #~ for i in range(256):
    for dwIndex in range(256):
        did = SP_DEVICE_INTERFACE_DATA()
        did.cbSize = ctypes.sizeof(did)

        if not SetupDiEnumDeviceInterfaces(
            g_hdi,
            None,
            ctypes.byref(GUID_CLASS_USBPRINT),
#            ctypes.byref(GUID_CLASS_COMPORT),
            dwIndex,
            ctypes.byref(did) ):
            if ctypes.GetLastError() != ERROR_NO_MORE_ITEMS:
                raise ctypes.WinError()
            break

        dwNeeded = DWORD()

        # get the size
        if not SetupDiGetDeviceInterfaceDetail(
            g_hdi,
            ctypes.byref(did),
            None, 0, ctypes.byref(dwNeeded),
            None ):
            # Ignore ERROR_INSUFFICIENT_BUFFER
            if ctypes.GetLastError() != ERROR_INSUFFICIENT_BUFFER:
                raise ctypes.WinError()

        # allocate buffer
        class SP_DEVICE_INTERFACE_DETAIL_DATA_A(ctypes.Structure):
            _fields_ = [
                ('cbSize', DWORD),
                ('DevicePath', CHAR*(dwNeeded.value - ctypes.sizeof(DWORD))),
            ]
            def __str__(self):
                return "DevicePath:%s" % (self.DevicePath,)

        idd = SP_DEVICE_INTERFACE_DETAIL_DATA_A()
        idd.cbSize = 5
        devinfo = SP_DEVINFO_DATA()
        devinfo.cbSize = ctypes.sizeof(devinfo)

        if not SetupDiGetDeviceInterfaceDetail(
            g_hdi,
            ctypes.byref(did),
            ctypes.byref(idd), dwNeeded, None,
            ctypes.byref(devinfo) ):
            raise ctypes.WinError()

        # hardware ID
        szHardwareID = ctypes.create_string_buffer('\0' * 250)
        if not SetupDiGetDeviceRegistryProperty(
            g_hdi,
            ctypes.byref(devinfo),
            SPDRP_HARDWAREID,
            None,
            ctypes.byref(szHardwareID), ctypes.sizeof(szHardwareID) - 1,
            None ):
            # Ignore ERROR_INSUFFICIENT_BUFFER
            if ctypes.GetLastError() != ERROR_INSUFFICIENT_BUFFER:
                raise ctypes.WinError()

        # davep ; stop here because printers don't seem to have a friendly name
        yield idd.DevicePath, "", szHardwareID.value

    SetupDiDestroyDeviceInfoList(g_hdi)