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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 data(self, index, role=Qt.DisplayRole):
 """Retrieve the data stored in the model at the given `index`. Args: index (QtCore.QModelIndex):
 The model index, which points at a data object. role (Qt.ItemDataRole, optional):
 Defaults to `Qt.DisplayRole`. You have to use different roles to retrieve different data for an `index`. Accepted roles are `Qt.DisplayRole`, `Qt.EditRole` and `DTYPE_ROLE`. Returns: None if an invalid index is given, the role is not accepted by the model or the column is greater than `1`. The column name will be returned if the given column number equals `0` and the role is either `Qt.DisplayRole` or `Qt.EditRole`. The datatype will be returned, if the column number equals `1`. The `Qt.DisplayRole` or `Qt.EditRole` return a human readable, translated string, whereas the `DTYPE_ROLE` returns the raw data type. """


        # an index is invalid, if a row or column does not exist or extends
        # the bounds of self.columnCount() or self.rowCount()
        # therefor a check for col>1 is unnecessary.
        if not index.isValid():
            return None

        col = index.column()

        #row = self._dataFrame.columns[index.column()]
        columnName = self._dataFrame.columns[index.row()]
        columnDtype = self._dataFrame[columnName].dtype

        if role == Qt.DisplayRole or role == Qt.EditRole:
            if col == 0:
                if columnName == index.row():
                    return index.row()
                return columnName
            elif col == 1:
                return SupportedDtypes.description(columnDtype)
        elif role == DTYPE_ROLE:
            if col == 1:
                return columnDtype
            else:
                return None