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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 id_for(self, city_name):
 """ Returns the long ID corresponding to the first city found that matches the provided city name. The lookup is case insensitive. .. deprecated:: 3.0.0 Use :func:`ids_for` instead. :param city_name: the city name whose ID is looked up :type city_name: str :returns: a long or ``None`` if the lookup fails """

        line = self._lookup_line_by_city_name(city_name)
        return int(line.split(",")[1]) if line is not None else None