Using a Python module generated with Boost: did not match C++ signature

Question

I am using a software called Mitsuba. It comes along with a Python implementation, wrapped with Boost. This line in Python:

scene = SceneHandler.loadScene(fileResolver.resolve("model.xml"), paramMap)

yields an error. The type of fileResolver.resolve is fs::path and the type of paramMap is ParameterMap according to the documentation.

The function signature in the C++ code is:

SceneHandler::loadScene(const fs::path &filename, const ParameterMap &params)

The error is:

Traceback (most recent call last):
  File "...\foo.py", line 22, in <module>
    scene = SceneHandler.loadScene(fileResolver.resolve("model.xml"), paramMap)
ArgumentError: Python argument types in
    SceneHandler.loadScene(str, StringMap)
did not match C++ signature:
    loadScene(class boost::filesystem2::basic_path<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >,struct boost::filesystem2::path_traits>, class std::map<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >,class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >,struct mitsuba::SimpleStringOrdering,class std::allocator<struct std::pair<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > const ,class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > > > >)

What further investigations can I make? Do you know where the problem comes from?

Ray · Accepted Answer · 2012-06-05 21:05:41Z

2

Unfortunately it's not clear which of the arguments is causing a problem.

According to the error message you have, the return type of fileResolver.resolve is apparently str, not boost::filesystem::basic_path. What you want to look at is where Mitsuba defines its Boost.Python interface to see if there is a "converter" registered for turning Python strings into boost::fs::path objects. If not, you'll have to figure out what the right way of getting a Python object that's convertible to the correct type is for this library.

For the second argument, you have basically the same checks to make, unless StringMap is already a Boost.Python type (what does type(paramMap.__class__) return?). It looks like ParameterMap is a typedef for

`std::map<std::string, std::string, mitsuba::SimpleStringOrdering>`

But again, there must be a Boost.Python converter registered that can do the conversion from the Python type.

answered Jun 5, 2012 at 21:05

Ray

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4 Comments

Flavian Hautbois Over a year ago

So type(paramMap.__class__) returns <type 'Boost.Python.class'>, so it shouldn't be a problem in the python file. Let me check the rest.

Flavian Hautbois Over a year ago

type(fileResolver.__class__) returns the same. What does a "converter" look like?

Ray Over a year ago

But type(fileResolver.resolve("model.xml")) is just str, right? Then that's the one with the missing from-Python converter. Looking at the Mitsuba source, there is a to-Python converter for fs::path, and this asymmetry is the source of the problem you're having. You should probably report this as a bug.

Flavian Hautbois Over a year ago

Do you mean there is something missing in those lines? bp::to_python_converter<fs::path, path_to_python_str>(); bp::implicitly_convertible<std::string, fs::path>();

Wenzel Jakob · Accepted Answer · 2013-11-22 11:11:03Z

0

Note that this bug has been fixed for a while now—there is now an implicit conversion that goes both ways between fs::path and std::string when crossing the C++/Python barrier.

answered Nov 22, 2013 at 11:11

Wenzel Jakob

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