Method returns prepared request query for Yahoo YQL API.

def prepare_query(self, symbol,  start_date, end_date):
        """Method returns prepared request query for Yahoo YQL API."""
        query = \
            'select * from yahoo.finance.historicaldata where symbol = "%s" and startDate = "%s" and endDate = "%s"' \
            % (symbol, start_date, end_date)

        return query