for Toster

class NewItemProxyModel(QtGui.QAbstractProxyModel):
    def __init__(self, new, parent=None, *args):
        super(NewItemProxyModel, self).__init__(parent, *args)
        self.__element__ = new


    def setSourceModel(self, model):

        self.beginResetModel()

        QtGui.QAbstractProxyModel.setSourceModel(self, model)

        model.dataChanged.connect(self.sourceDataChanged)
        model.modelReset.connect(self.sourceModelReset)

        # required for filtering/sorting
        model.rowsInserted.connect(self.sourceRowsInserted)
        model.rowsRemoved.connect(self.sourceRowsRemoved)
        model.rowsAboutToBeInserted.connect(self.sourceRowsAboutToBeInserted)
        model.rowsAboutToBeRemoved.connect(self.sourceRowsAboutToBeRemoved)
        model.layoutAboutToBeChanged.connect(self.sourceLayoutAboutToBeChanged)
        model.layoutChanged.connect(self.sourceLayoutChanged)

        self.endResetModel()

# ...

    def mapToSource(self, proxy_index):

        if not proxy_index.isValid():
            return QtCore.QModelIndex()

        if proxy_index.row() == 0:
            # return self.createIndex(proxy_index.row(), proxy_index.column(), proxy_index.parent())
            return self.createIndex(proxy_index.row(), proxy_index.column())

        else:
            return self.sourceModel().index(proxy_index.row() - 1, proxy_index.column())
            # return self.sourceModel().createIndex(proxy_index.row() - 1, proxy_index.column(), proxy_index.internalPointer())


    def mapFromSource(self, source_index):

        if not source_index.isValid():
            return QtCore.QModelIndex()

        return self.index(source_index.row() + 1, source_index.column())
        # return self.createIndex(source_index.row() + 1, source_index.column(), source_index.internalPointer())


    def rowCount(self, parent=QtCore.QModelIndex()):

        return self.sourceModel().rowCount() + 1


    def data(self, index, role=QtCore.Qt.DisplayRole):

        if index.isValid():
            if index.row() == 0:
                if role == QtCore.Qt.DisplayRole: # or role == QtCore.Qt.EditRole:
                    value = '<new %s>' % (self.__element__.name, )
                    return QtCore.QVariant(value)

            else:
                if role == QtCore.Qt.DisplayRole: # or role == QtCore.Qt.EditRole:
                    value = self.mapToSource(index).data(role)
                    return QtCore.QVariant(value)

        return QtCore.QVariant()