qteasy/database.py
def date_range(self):
        """ return the date range of existing data

        :return:
        """
        return None
 return the date range of existing data

        :return:
        
return the date range of existing data
return the date range of existing data
def date_range(self):
        return None
def date_range ( self ) : return None
return the date range of existing data
return the date range of existing data
""" return the date range of existing data

        :return:
        """
None
self