Python, std_wstring.i and %import

I encountered an unexpected problem when using std_wstring.i in some 
SWIG Python modules. Module B uses %import to get definitions from 
module A, and both modules contain %include "std_wstring.i". During 
compilation of Module B (on Windows) I got "error C3861: 
'SWIGPY_UNICODE_ARG': identifier not found". Module A compiles without a 
problem.

SWIGPY_UNICODE_ARG is defined in pywstrings.swg inside %{ %} brackets. 
It appears that when module A is imported into module B the contents of 
pywstrings.swg are imported with it, but without the SWIGPY_UNICODE_ARG 
definition. (I assume that's what's happening, but I don't fully 
understand SWIG's various import & include directives.)

My solution has been to wrap the use of std_wstring.i in SWIGIMPORTED 
guards:

#ifndef SWIGIMPORTED
%include "std_wstring.i"
#endif

I'm now wondering why I haven't run into similar problems with other 
SWIG library modules.
-- 
Jim Easterbrook                 <http://www.jim-easterbrook.me.uk/>