def swig_sources(self, sources, extension):
        """Walk the list of source files in 'sources', looking for SWIG
        interface (.i) files.  Run SWIG on all that are found, and
        return a modified 'sources' list with SWIG source files replaced
        by the generated C (or C++) files.
        """
        new_sources = []
        swig_sources = []
        swig_targets = {}

        # XXX this drops generated C/C++ files into the source tree, which
        # is fine for developers who want to distribute the generated
        # source -- but there should be an option to put SWIG output in
        # the temp dir.

        if self.swig_cpp:
            log.warning("--swig-cpp is deprecated - use --swig-opts=-c++")

        if (
            self.swig_cpp
            or ('-c++' in self.swig_opts)
            or ('-c++' in extension.swig_opts)
        ):
            target_ext = '.cpp'
        else:
            target_ext = '.c'

        for source in sources:
            (base, ext) = os.path.splitext(source)
            if ext == ".i":  # SWIG interface file
                new_sources.append(base + '_wrap' + target_ext)
                swig_sources.append(source)
                swig_targets[source] = new_sources[-1]
            else:
                new_sources.append(source)

        if not swig_sources:
            return new_sources

        swig = self.swig or self.find_swig()
        swig_cmd = [swig, "-python"]
        swig_cmd.extend(self.swig_opts)
        if self.swig_cpp:
            swig_cmd.append("-c++")

        # Do not override commandline arguments
        if not self.swig_opts:
            for o in extension.swig_opts:
                swig_cmd.append(o)

        for source in swig_sources:
            target = swig_targets[source]
            log.info("swigging %s to %s", source, target)
            self.spawn(swig_cmd + ["-o", target, source])

        return new_sources
Walk the list of source files in 'sources', looking for SWIG
        interface (.i) files.  Run SWIG on all that are found, and
        return a modified 'sources' list with SWIG source files replaced
        by the generated C (or C++) files.
        
product/gradle-plugin/src/main/python/setuptools/_distutils/command/build_ext.py