Load database for gffutils. 

    Parameters
    ----------
    f : str
        Path to database.

    Returns
    -------
    db : gffutils.FeatureDB
        gffutils feature database.

def load_gffutils_db(f):
    """
    Load database for gffutils. 

    Parameters
    ----------
    f : str
        Path to database.

    Returns
    -------
    db : gffutils.FeatureDB
        gffutils feature database.

    """
    import gffutils
    db = gffutils.FeatureDB(f, keep_order=True)
    return db