CODEWITHSUNDEEP
pythonc++swig
Totte Karlsson
Totte Karlsson

Reputation: 1341

Change return value type of Python swigged C function

I have a C++ function 

Version getVersion(){ return Version("1.2.3.5");}

where Version is a class, holding "Version information", e.g.

class Version
{
    public:
                                                Version(const string& version = gEmptyString);
        bool                                    parse(const string& input);
        int                                     getMajor() const;
        int                                     getMinor() const;
        int                                     getPatch() const;
        int                                     getBuild() const;
        string                                  asString(const string& format = gEmptyString) const;


    private:
        int                                     mMajor;
        int                                     mMinor;
        int                                     mPatch;
        int                                     mBuild;
};

When wrapping this code using Swig, a Python user get a Version object back when calling the getVersion() function.

I would want to change the behavior of the getVersion() function when called from Python. Instead of returning a Version object, I would want to return a string, representing the Version value.

I tried the following:

%rename(getVersionHidden) getVersion;

%inline %{
std::string getVersion()
{
    Version v = getVersionHidden();
    return v.asString();
}
%}

but that does not compile:

   Error ... Call to undefined function 'getVersionHidden' in function 
   getVersion()
   Error E2285 P:\builds\dsl\wrappers\python\dslPYTHON_wrap.cxx 4434: Could not 
   find a match for 'Version::Version(const Version&)' in function getVersion()
   Error E2015 P:\builds\dsl\wrappers\python\dslPYTHON_wrap.cxx 16893: Ambiguity 
   between 'dsl::getVersion() at P:/libs/dsl/Common\dslCommon.h:8' and 
   'getVersion() at P:\builds\dsl\wrappers\python\dslPYTHON_wrap.cxx:4432' in 
   function _wrap_getVersionHidden(_object *,_object *)

Perhaps usage of a typemap is the way to go. I'm new to Swig so not sure..?

Upvotes: 1

Views: 299

Answers (1)

Zrax
Zrax

Reputation: 1670

%rename only renames the function for the target language -- that is, %rename("getVersionHidden") getVersion; will create a Python function (getVersionHidden) which forwards the getVersion() defined in C/C++.

Instead, you should create a new function and then rename that to override the getVersion that would otherwise get generated automatically:

%rename("getVersion") _getVersion_Swig;

%inline %{
std::string _getVersion_Swig()
{
    Version v = getVersion();
    return v.asString();
}
%}

Upvotes: 1

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