def __parse_s3_uri(uri):
    """Parse s3 uri into bucket and key `tuple`

    Parameters
    ----------
        s3_uri: `str`
            URI for s3 object of the form `s3://<bucket>/some/path`
    Returns
    -------
    bucket, key `tuple`
    """
    if not uri.startswith('s3://'):
        raise Exception('Invalid S3 URI')
    bucket = uri[len('s3://'):].split('/')[0]
    key = uri[len('s3://' + bucket):]
    return bucket, key