In wxPython, Grid.GridCellBoolEditor() always return empty string

Question

Here is my code:

class CustomGrid(grid.Grid):
    def __init__(self, parent):
        gridlib.Grid.__init__(self, parent, pos=wx.DefaultPosition, size=wx.Size(-1, 580))
        self.CreateGrid(1, 7)
        self.SetRowLabelSize(200)
        self.SetRowLabelAlignment(wx.ALIGN_LEFT, wx.ALIGN_CENTER)
        self.SetColLabelAlignment(wx.ALIGN_CENTER, wx.ALIGN_CENTER)
        # self.SetCellHighlightPenWidth(0)
        # self.SetCellHighlightROPenWidth(0)

        days = weekDaysFr()
        for (k, day) in days.items():
            self.SetColLabelValue(k, day)
        self.SetCellRenderer(0, 0, grid.GridCellBoolRenderer())
        self.SetCellEditor(0, 0, grid.GridCellBoolEditor())
        self.SetCellValue(0, 0, '0')
        self.SetCellAlignment(0, 0, wx.ALIGN_CENTRE, wx.ALIGN_CENTRE)

        self.Bind(gridlib.EVT_GRID_CELL_LEFT_CLICK, self.onGridCellClick)