Return a tuple (converter_func, converter_type). The converter function converts a list into a numpy array of the given numpy_type. This type must be a valid numpy type, e.g. numpy.int, numpy.uint, numpy.int8, numpy.int64, numpy.float, numpy.float64, numpy.str. The converter type is used to track the generic data type (int, float, str) that is produced by the converter function.