Question

I have some C++ methods that have std::set<std::string> as argument or return value.
I would like to map this to a Python frozenset (or regular set) but there does not seem to be a straightforward way to do this.
Does anyone know how one may accomplish this task.

Answer 1

Unfortunately, the standard indexing_suite from Boost.Python does not support std::set. There is a indexing_suite v2, that works on all stl containers. (http://mail.python.org/pipermail/cplusplus-sig/2009-July/014704.html)

It may not have made it to the official distribution, but you can find it by asking around.
(http://mail.python.org/pipermail/cplusplus-sig/2009-July/014691.html)

I found it to be harder to use then the original indexing_suite, but it might fit your needs.

If that does not work, you can just manually wrap std::set<std::string> like you would any other class. This will get you a std::set<std::string> into python, where you can turn it into a python set fairly easily.

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I think that both of those are more work then is called for though. Here is what I would do:

First, wrap the function in C++ with one that has the same signature, but stuffs the returned data in to a std::vector<std::string> instead of a std::set<std::string>. expose that function rather then the original

Now you have the data in python.

Second, wrap the c++ function in python function that takes the data in that std::vector<std::string> and stuffs it into a python set.

Yes, this is rather silly from a design aesthetics point of view, and not the most performant code in the world, but is gets you to where you are going with a minimum of code, and it is fairly robust.