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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def db_url(self, var=DEFAULT_DATABASE_ENV, default=NOTSET, engine=None):
 """Returns a config dictionary, defaulting to DATABASE_URL. :rtype: dict """

        return self.db_url_config(self.get_value(var, default=default), engine=engine)