Minimal Qt example of adding a "virtual row" via a proxy model

qt_proxy_model.py

#!/usr/bin/env python
"""
Refs: 
"[Maya-Python] Customized display of files/folders in a QTreeView that is using QFileSystemModel."
https://groups.google.com/d/topic/python_inside_maya/TaFm2yNToJ8/discussion
"""

from PySide import QtCore, QtGui


class VirtualRowProxyModel(QtGui.QSortFilterProxyModel):

    # Some internal id indicating when its a virtual row
    IS_VIRTUAL = -1

    def mapToSource(self, proxyIndex):
        if self._isVirtualRow(proxyIndex):
            return QtCore.QModelIndex()

        return super(VirtualRowProxyModel, self).mapToSource(proxyIndex)

    def index(self, row, column, parent=QtCore.QModelIndex()):
        model = self.sourceModel()
        sourceParent = self.mapToSource(parent)

        sourceRows = model.rowCount(sourceParent)
        if row >= sourceRows:
            return self.createIndex(row, column, self.IS_VIRTUAL)

        return super(VirtualRowProxyModel, self).index(row, column, parent)

    def parent(self, index):
        if self._isVirtualRow(index):
            return QtCore.QModelIndex()
        return super(VirtualRowProxyModel, self).parent(index)

    def data(self, proxyIndex, role=QtCore.Qt.DisplayRole):
        if self._isVirtualRow(proxyIndex):
            if role == QtCore.Qt.DisplayRole:
                return "-VIRTUAL ROW-"
            return None
        return super(VirtualRowProxyModel, self).data(proxyIndex, role)

    def rowCount(self, parent=QtCore.QModelIndex()):
        return self.sourceModel().rowCount(self.mapToSource(parent)) + 1

    def _isVirtualRow(self, index):
        return index.isValid() and index.internalId() == self.IS_VIRTUAL


if __name__ == '__main__':
    app = QtGui.QApplication([])

    view = QtGui.QTreeView()

    model = QtGui.QStandardItemModel()
    model.appendRow(QtGui.QStandardItem("A"))
    model.appendRow(QtGui.QStandardItem("B"))
    model.appendRow(QtGui.QStandardItem("C"))

    proxy = VirtualRowProxyModel()
    proxy.setSourceModel(model)

    view.setModel(proxy)

    view.resize(800, 600)
    view.show()
    view.raise_()

    app.exec_()