def is_obsolete(obo_tags):
    """ checks if an "is_obsolete" flag is in the tags for an obo entry
    
    Args:
        obo_tags: tags for an obo entry
    
    Returns:
        True/False for whether the entry is obsolete
    """
    return 'is_obsolete' in obo_tags and str(obo_tags['is_obsolete'][0]
        ) == 'true'
