On Sun, 5 Jul 2009, Bo Peng wrote:
> I have a C++ class that is wrapped into a Python shadow class. In
> addition to regular Python input (say, a number), I would like to
> allow users to pass None from the user interface and tells the C++
> class no invalid input is given. It is more or less like using -1 as a
> default parameter when only positive numbers are allowed.
>
> However, SWIG does not seem to allow such usage because it will not
> pass None to the C++ class even if it accepts such an input (e.g. with
> a constructor that accepts a PyObject * object). Whenever I pass None,
> I would get an error message such as "Invalid null reference".
My understanding/recollection is that None is acceptable for any pointer
type (and is converted to a null pointer), but is not acceptable for a
reference (which makes sense). I'm not clear on the details of what
you're doing, but that would appear to be the cause of that error message.
This behavior is dictated by the standard typemaps for pointers and
references.
Josh
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