def get(
        self,
        link,            # type: Link
        package_name,    # type: Optional[str]
        supported_tags,  # type: List[Tag]
    ):
        # type: (...) -> Link
        """Returns a link to a cached item if it exists, otherwise returns the
        passed link.
        """
        raise NotImplementedError()
Returns a link to a cached item if it exists, otherwise returns the
        passed link.
        
product/gradle-plugin/src/main/python/pip/_internal/cache.py