'Return current value'

def get_value(self, index):

    if (index.column() == 0):
        return self.keys[index.row()]
    elif (index.column() == 1):
        return self.types[index.row()]
    elif (index.column() == 2):
        return self.sizes[index.row()]
    else:
        return self._data[self.keys[index.row()]]
