def get_ext_fullpath(self, ext_name):
        """Returns the path of the filename for a given extension.

        The file is located in `build_lib` or directly in the package
        (inplace option).
        """
        fullname = self.get_ext_fullname(ext_name)
        modpath = fullname.split('.')
        filename = self.get_ext_filename(modpath[-1])

        if not self.inplace:
            # no further work needed
            # returning :
            #   build_dir/package/path/filename
            filename = os.path.join(*modpath[:-1] + [filename])
            return os.path.join(self.build_lib, filename)

        # the inplace option requires to find the package directory
        # using the build_py command for that
        package = '.'.join(modpath[0:-1])
        build_py = self.get_finalized_command('build_py')
        package_dir = os.path.abspath(build_py.get_package_dir(package))

        # returning
        #   package_dir/filename
        return os.path.join(package_dir, filename)
Returns the path of the filename for a given extension.

        The file is located in `build_lib` or directly in the package
        (inplace option).
        
product/gradle-plugin/src/main/python/setuptools/_distutils/command/build_ext.py