@classmethod
def from_uri(cls, uri):
    """
        from_uri class method create a class instance from url

        >> from gcspath import PureGCSPath
        >> PureGCSPath.from_url('gs://<bucket>/')
        << PureGCSPath('/<bucket>')
        """
    if not uri.startswith('gs://'):
        raise ValueError('...')
    return cls(uri[4:])
