PySide QDataWidgetMapper multiple delegates

#!/usr/bin/env python2
# -*- coding: utf-8 -*-
import sys
from datetime import date

from PySide import QtGui, QtCore
from PySide.QtCore import Qt

def setup_model():

    class TestModel(QtCore.QAbstractTableModel):

        def __init__(self, columns, rows):
            QtCore.QAbstractTableModel.__init__(self)
            self.rows = rows
            self.columns = columns

        def columnCount(self, index):
            return len(self.columns)

        def rowCount(self, index):
            return len(self.rows)

        def data(self, index, role):
            if index.isValid():
                field_id = self.columns[index.column()]
                value = getattr(self.rows[index.row()],field_id)
                if (role == Qt.EditRole) or (role == Qt.DisplayRole) or (role == Qt.ToolTipRole):
                    return value

        def setData(self, index, value, role=Qt.EditRole):
            if index.isValid() and role == Qt.EditRole:
                field_id = self.columns[index.column()]
                setattr(self.rows[index.row()], field_id, value)
                return True


    class Person(object):
        def __init__(self, name, birthday):
            self.name = name
            self.birthday = birthday

    fields = ['name', 'birthday']
    rows = [
        Person(u'Peter Ivanov', date(1976, 12, 1)),
        Person(u'Masha Poryvayeva', date(1982, 03, 14)),
        Person(u'Helge Seppälla', date(1979, 8, 15))
    ]

    return TestModel(fields, rows)

class DateDelegate(QtGui.QStyledItemDelegate):

    def __init__(self, parent = None):
        QtGui.QStyledItemDelegate.__init__(self, parent)

    def createEditor(self, parent, option, index):
        pass

    def setEditorData(self, dateEdit, index):
        value = index.model().data(index, QtCore.Qt.EditRole)
        if value:
            dateEdit.setDate(QtCore.QDate(value.year, value.month, value.day))

    def setModelData(self, dateEdit, model, index):
        value = dateEdit.date()
        model.setData(index, value.toPython())


class LineDelegate(QtGui.QStyledItemDelegate):

    def __init__(self, parent = None):
        QtGui.QStyledItemDelegate.__init__(self, parent)

    def createEditor(self, parent, option, index):
        pass

    def setEditorData(self, editor, index):
        editor.setText(index.model().data(index, QtCore.Qt.EditRole))

    def setModelData(self, editor, model, index):
        model.setData(index, editor.text(), QtCore.Qt.EditRole)


class DelegateProxy(QtGui.QStyledItemDelegate):

    #that's the delegate proxy, forwarding data to real delegates that will handle it properly
    def __init__(self, delegates, parent=None):
        QtGui.QStyledItemDelegate.__init__(self, parent)
        self.delegates = delegates

    def setEditorData(self, editor, index):
    #that is kinda naive and depends on column order in the model.
    #you should implement your own, more reliable way to link item index
    #and a delegate, responsible for handling the item
        delegate = self.delegates[index.column()]
        delegate.setEditorData(editor, index)

    def setModelData(self, editor, model, index):
        delegate = self.delegates[index.column()]
        delegate.setModelData(editor, model, index)

class MyEditWindow(QtGui.QWidget):

    def __init__(self):
        QtGui.QWidget.__init__(self)
        self.setLayout(QtGui.QFormLayout(self))
        self.model = setup_model()
        self.data_mapper = QtGui.QDataWidgetMapper(self)
        self.data_mapper.setModel(self.model)
        #creating widgets
        self.name = QtGui.QLineEdit(self)
        self.layout().addRow('Name:', self.name)

        self.birthday = QtGui.QDateEdit(self)
        self.layout().addRow('Birthday:', self.birthday)

        #and mapping them
        self.data_mapper.addMapping(self.name, 0)
        self.data_mapper.addMapping(self.birthday, 1)
        #setting up multiple delegates
        delegates = [LineDelegate(self), DateDelegate(self)]
        self.data_mapper.setItemDelegate(DelegateProxy(delegates, self))
        self.data_mapper.toFirst()
        #additional stuff
        self.btn_prev = QtGui.QPushButton('Prev.', self)
        self.btn_prev.clicked.connect(self.data_mapper.toPrevious)
        self.btn_next = QtGui.QPushButton('Next', self)
        self.btn_next.clicked.connect(self.data_mapper.toNext)

        self.buttons_layout = QtGui.QHBoxLayout()
        self.layout().addRow(self.buttons_layout)
        self.buttons_layout.addWidget(self.btn_prev)
        self.buttons_layout.addWidget(self.btn_next)

if __name__ == '__main__':
    app = QtGui.QApplication(sys.argv)
    window = MyEditWindow()
    window.show()
    app.exec_()