def user_exists(self, username, login_from='%'):
        return login_from in self.get_user_hosts(username)
http://trac.edgewall.org/ticket/4247
dataset/ETHPy150Open python-provy/provy/provy/more/centos/database/mysql.py/MySQLRole.user_exists--crossover with--dataset/ETHPy150Open edgewall/trac/trac/ticket/tests/model.py/VersionTestCase.test_exists