AccessSelections() Problem

Dear all,

I have part document (not assembly), according to the api, I should set the Component argument of AccessSelections( topDoc, Component) to 'Nothing' when it is a part document. But The problem is that I am writing the code in python and when I set Component to 'None' it raises and error, it might be because of not campatibility between 'Nothing' in VB and 'None' in python. What should I do instead?
Note that I use 0 integer but it doesn't work again and also I use ctypes function c_void_p(None) but it also doesn't work and return an error and here the error:

sfd.AccessSelections(swModel,buffer(Nothing))
File ">", line 2, in AccessSelections
pywintypes.com_error: (-2147352571, 'Type mismatch.', None, 2)

Thanks,
Artman SolidworksApi macros