import csv

class CSVFieldUnknown(Exception):
    def __init__(self, cls, field):
        super(CSVFieldUnknown, self).__init__(
            "Unknown field %s for class %s" % (
                field,
                cls.__name__
            )
        )

class CSVEntry:
    _contents = {}
    def __init__(self, **kvargs):
        for field in self.__class__.fields:
            setattr(self, field, "")
        for field, val in kvargs.items():
            setattr(self, field, val)

    def __getattr__(self, key):
        if key not in self.__class__.fields:
            raise CSVFieldUnknown(self.__class__, key)
        return self._contents[key]

    def __setattr__(self, key, value):
        if key not in self.__class__.fields:
            raise CSVFieldUnknown(self.__class__, key)
        self._contents[key] = value

    @classmethod
    def fromRow(cls, row):
        assert len(row) == len(cls.fields)
        return cls(**{ field : value for field,value in zip(cls.fields, row)})

    def toRow(self):
        return list(getattr(self,field) for field in self.__class__.fields)

    @classmethod
    def loadFile(cls, file):
        with open(file) as csvfile:
            reader = csv.reader(csvfile)
            return list( cls.fromRow(row) for row in reader )

    @staticmethod
    def saveFile(file, entries):
        with open(file,"w") as csvfile:
            writer = csv.writer(csvfile)
            writer.writerows( entry.toRow() for entry in entries )