unsupported operand type(s) for +=: 'NoneType' and 'list' in invalidate_draw in chaco

OS: Windows XP 32, Windows 7 32
EPD: 7.0, 6.3
related issue: memory leak in copy_ticks on linux (to be submitted as next issue)

During refresh / update of a plot, we sometimes get the following error.

```
self._update_region += damaged_regions

TypeError: unsupported operand type(s) for +=: 'NoneType' and 'list'
```

The respective code in AbstractWindow reads:

```
class AbstractWindow(HasTraits):
...
def invalidate_draw(self, damaged_regions=None, self_relative=False):
if damaged_regions is not None and self._update_region is not None:
self._update_region += damaged_regions
else:
self._update_region = None
```

Thus, the error in principle cannot occur. Now I speculate: is it a race condition? Is there something not thread safe here?

Sometimes the error occurs frequently and crashes the code. It looks like there is also a memory leak.

In the following are the tracebacks with and without memory error.

Without memor error:

2010-09-06 12:45:16,640 - trait_notifiers._log_exception - ERROR - Exception occurred in traits notification handler for object: , trait: data_changed, old value: , new value: True Traceback (most recent call last):

File "C:\Python26\lib\site-packages\enthought\traits\trait_notifiers.py", line 481, in rebind_call_0

self.dispatch( getattr( self.object(), self.name ) )

File "C:\Python26\lib\site-packages\enthought\traits\trait_notifiers.py", line 424, in dispatch

handler( *args )

File "C:\Python26\lib\site-packages\enthought\chaco\base_xy_plot.py", line 600, in _either_data_changed

self.invalidate_draw()

File "C:\Python26\lib\site-packages\enthought\enable\component.py", line 549, in invalidate_draw

self.container.invalidate_draw(damaged_regions=damaged_regions, self_relative=True)

File "C:\Python26\lib\site-packages\enthought\enable\component.py", line 552, in invalidate_draw

self._window.invalidate_draw(damaged_regions=damaged_regions, self_relative=True)

File "C:\Python26\lib\site-packages\enthought\enable\abstract_window.py", line 230, in invalidate_draw

self._update_region += damaged_regions

TypeError: unsupported operand type(s) for +=: 'NoneType' and 'list'

With Memory Error:

MemoryError Traceback (most recent call last)

C:\Python26\lib\site-packages\enthought\enable\abstract_window.pyc in _paint(sel f, event)

348 self.component.do_layout() 349 gc = self._gc

--> 350 self.component.draw(gc, view_bounds=(0, 0, size[0], size[1]))

351 352 # damaged_regions = draw_resultdamaged_regions?

C:\Python26\lib\site-packages\enthought\enable\component.pyc in draw(self, gc, v iew_bounds, mode)

423 self.do_layout() 424

--> 425 self._draw(gc, view_bounds, mode)

426 return 427

C:\Python26\lib\site-packages\enthought\enable\component.pyc in _draw(self, gc, view_bounds, mode)

759 else: 760 for layer in self.draw_order:

--> 761 self._dispatch_draw(layer, gc, view_bounds, mode)

762 763 return

C:\Python26\lib\site-packages\enthought\enable\container.pyc in _dispatch_draw(s elf, layer, gc, view_bounds, mode)

324 component._draw(gc, new_bounds, mode) 325 else:

--> 326 component._dispatch_draw(layer, gc, new_bounds, mode)

327 finally: 328 gc.restore_state()

C:\Python26\lib\site-packages\enthought\enable\component.pyc in _dispatch_draw(s elf, layer, gc, view_bounds, mode)

779 handler = getattr(self, "_draw_" + layer, None) 780 if handler:

--> 781 handler(gc, view_bounds, mode)

782 return 783

C:\Python26\lib\site-packages\enthought\chaco\base_2d_plot.pyc in _draw_image(se lf, gc, view_bounds, mode)

202 Used by the PlotComponent interface. 203 """

--> 204 self._render(gc)

205 return 206

C:\Python26\lib\site-packages\enthought\chaco\cmap_image_plot.pyc in _render(sel f, gc)

87 self._compute_cached_image(self.value.metadata['selectio

n_masks'])

88 else:

---> 89 self._compute_cached_image()

90 ImagePlot._render(self, gc) 91

C:\Python26\lib\site-packages\enthought\chaco\cmap_image_plot.pyc in _compute_ca ched_image(self, selection_masks)

100 if not self._mapped_image_cache_valid: 101 cached_mapped_image = \

--> 102 self.value_mapper.map_screen(self.value.data) \* 255

103 if selection_masks is not None: 104 # construct a composite mask

C:\Python26\lib\site-packages\enthought\chaco\color_mapper.pyc in map_screen(sel f, data_array)

256 norm_data = clip((data_array - low) / (high - low), 0.0, 1.0

)

257

--> 258 return self._map(norm_data)

259 260

C:\Python26\lib\site-packages\enthought\chaco\color_mapper.pyc in _map(self, X)

402 403 nanmask = isnan(xa)

--> 404 xa = where(nanmask, 0, (xa \* (self.steps-1)).astype(int))

405 rgba = zeros(xa.shape+(4,), float) 406 rgba[...,0] = where(nanmask, 0, take(self._red_lut, xa))