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

        >> from s3path import PureS3Path
        >> PureS3Path.from_url('s3://<bucket>/')
        << PureS3Path('/<bucket>')
        """
    if not uri.startswith('s3://'):
        raise ValueError('...')
    return cls(uri[4:])
