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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def generate_handler_sourcepath( self, toolchain, spec, loaderplugin_sourcepath):
 """ Attempt to locate the plugin source; returns a mapping of modnames to the absolute path of the located sources. """


        # TODO calmjs-4.0.0 consider formalizing to the method instead
        npm_pkg_name = (
            self.node_module_pkg_name
            if self.node_module_pkg_name else
            self.find_node_module_pkg_name(toolchain, spec)
        )

        if not npm_pkg_name:
            cls = type(self)
            registry_name = getattr(
                self.registry, 'registry_name', '<invalid_registry/handler>')
            if cls is NPMLoaderPluginHandler:
                logger.error(
                    "no npm package name specified or could be resolved for "
                    "loaderplugin '%s' of registry '%s'; please subclass "
                    "%s:%s such that the npm package name become specified",
                    self.name, registry_name, cls.__module__, cls.__name__,
                )
            else:
                logger.error(
                    "no npm package name specified or could be resolved for "
                    "loaderplugin '%s' of registry '%s'; implementation of "
                    "%s:%s may be at fault",
                    self.name, registry_name, cls.__module__, cls.__name__,
                )
            return {}

        working_dir = spec.get(WORKING_DIR, None)
        if working_dir is None:
            logger.info(
                "attempting to derive working directory using %s, as the "
                "provided spec is missing working_dir", toolchain
            )
            working_dir = toolchain.join_cwd()

        logger.debug("deriving npm loader plugin from '%s'", working_dir)

        target = locate_package_entry_file(working_dir, npm_pkg_name)
        if target:
            logger.debug('picked %r for loader plugin %r', target, self.name)
            # use the parent recursive lookup.
            result = super(
                NPMLoaderPluginHandler, self).generate_handler_sourcepath(
                    toolchain, spec, loaderplugin_sourcepath)
            result.update({self.name: target})
            return result

        # the expected package file is not found, use the logger to show
        # why.
        # Also note that any inner/chained loaders will be dropped.
        if exists(join(
                working_dir, 'node_modules', npm_pkg_name,
                'package.json')):
            logger.warning(
                "'package.json' for the npm package '%s' does not contain a "
                "valid entry point: sources required for loader plugin '%s' "
                "cannot be included automatically; the build process may fail",
                npm_pkg_name, self.name,
            )
        else:
            logger.warning(
                "could not locate 'package.json' for the npm package '%s' "
                "which was specified to contain the loader plugin '%s' in the "
                "current working directory '%s'; the missing package may "
                "be installed by running 'npm install %s' for the mean time "
                "as a workaround, though the package that owns that source "
                "file that has this requirement should declare an explicit "
                "dependency; the build process may fail",
                npm_pkg_name, self.name, working_dir,
                npm_pkg_name,
            )

        return {}