[C++-sig] Overriding operator == and = for None

Ralf W. Grosse-Kunstleve rwgk at yahoo.com
Wed Jun 21 22:49:32 CEST 2006

I think you can do what you want based on boost::optional. You may want to look
here for an example:


Note that "x is None" works correctly, not just "x == None".

The boost::optional documentation is here:


Feel free to copy optional_conversions.h if you are interested.

--- Will Lee <lee.will at gmail.com> wrote:

> Is there a way I can override the operator == and = for a wrapped c++ object
> to take in a Python None type?  Essentially, I'd like to define a class
> where it can do:
> #NullableInt is a struct that holds an int and a boolean, indicating whether
> it is valid or not
> c = NullableInt(3)
> # NullableInt wraps a C++ std::vector<NullableInt>
> cv = NullableIntVec()
> cv.append(c) # ok
> cv[0] = None
> print cv[0]
> # should print out "None", and the C++'s struct would hold a boolean that's
> set to false
> # Generates an invalid Int
> cInvalid = NullableInt()
> # Should be true, it won't remove object but setting the underlying c++
> object to None)
> cv[0] == cInvalid
> # Should also be true if we can override ==
> cv[0] == None
> Does anybody know if it is posslbe in Boost.Python to have this behavior?
> Will

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