wxPython segmentation fault with Editors

Question

I have created a wx.grid.Grid with a wx.grid.PyGridTableBase derived class to provide its data. I want to also to control the editors used on the table. Towards that end I defined the following method

def GetAttr(self, row, col, kind):
    attr = wx.grid.GridCellAttr()
    if col == 0:
        attr.SetEditor( wx.grid.GridCellChoiceEditor() )
    return attr

However, this causes a segmentation fault whenever I attempt to created the editor in the grid. I did try creating the editor beforehand and passing it in as a parameter but received the error:

    TypeError: in method 'GridCellAttr_SetEditor', expected argument 2 of type 
'wxGridCellEditor *'

I suspect the second error is caused by the GridCellAttr taking ownership off and then destroying my editor.

I also tried using the SetDefaultEditor method on the wx.grid.Grid and that works, but naturally does not allow me to have a column specific editing strategy.

See Full Example of crashing program: http://pastebin.com/SEbhvaKf

Answer 1

This should solve it:

import wx
import wx.grid as gridlib

and change:

def GetAttr(self, row, col, kind):
    attr = gridlib.GridCellAttr()
    if col == 0:
        attr.SetEditor( gridlib.GridCellChoiceEditor() )
    return attr

Obs: I have no idea why you need to do it this way because:

>>> import wx
>>> attr = wx.grid.GridCellAttr()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'module' object has no attribute 'grid'

Do not work but:

import wx.grid as gridlib
attr = gridlib.GridCellAttr()

works... but:

print attr
<wx.grid.GridCellAttr; proxy of <wx.grid.GridCellAttr; proxy of <Swig Object of type 'wxGridCellAttr *' at 0x97cb398> > >

It says: <wx.grid.GridCellAttr; proxy of <wx.grid.GridCellAttr>...> !

Obs2: if you use the ChoiceEditor on the whole column 0, you could also define it only one time before showing the grid with:

attr.SetEditor( gridlib.GridCellChoiceEditor() )
yourGrid.SetColAttr(0, attr)

and you could remove all the code from the GetAttr method (I think it should be faster - but i never timed that).

Answer 2

I figured out the problem:

The wxWidgets code assumes that the same Editor will be consistently returned from GetCellAttr. Returning a different editor each time as I was doing caused the segmentation faults.

In order to return the same editor multiple times I also need to call IncRef() on the editor to keep it alive.

For anybody else hitting the same problem in future, see my working code:

import wx.grid 

app = wx.PySimpleApp()

class Source(wx.grid.PyGridTableBase):
    def __init__(self):
        super(Source, self).__init__()
        self._editor = wx.grid.GridCellChoiceEditor()

    def IsEmptyCell(self, row, col):
        return False

    def GetValue(self, row, col):
        return repr( (row, col) )

    def SetValue(self, row, col, value):
        pass

    def GetNumberRows(self):
        return 5

    def GetNumberCols(self):
        return 5

    def GetAttr(self, row, col, kind):
        attr = wx.grid.GridCellAttr()
        self._editor.IncRef()
        attr.SetEditor( self._editor )
        return attr


frame = wx.Frame(None)
grid = wx.grid.Grid(frame)
grid.SetTable( Source() )
frame.Show()

app.MainLoop()