Hi. I think the example on volatile attributes given in "Advanced ZODB for Python Programmers" article shows a bad practice.
>From the article: if hasattr(self, '_v_image'): return self._v_image This should be rewritten as: try: return self._v_image except AttributeError: This solves cases where _v_ attribute gets garbage-collected between hasattr call and "return" line. A way to make this obvious is to artificially set object cache size to 0. Note that another broken pattern would be to use code like: self._v_image=expensive_calculation() return self._v_image the article advertises the right pattern (using a local variable for return): image=expensive_calculation() self._v_image=image return image I've been hitting problems with this code pattern many times in the past, and should have written about it earlier.  http://zodb.org/documentation/articles/ZODB2.html -- Vincent Pelletier _______________________________________________ For more information about ZODB, see the ZODB Wiki: http://www.zope.org/Wikis/ZODB/ ZODB-Dev mailing list - ZODB-Dev@zope.org https://mail.zope.org/mailman/listinfo/zodb-dev