[Zope-dev] Zope 2.3.1b1, strange things when ConflictError.

[Steve Alexander]

Erik,

You're returning a mutable object from methodB. You should either return 
an immutable object (such as a tuple or a string), or return a *copy* of 
your mutable object.

some_list.reverse() reverses the list in-place. That's why you're seeing 
the strange reversal results you report.

The easiest way to achieve this is to change methodA as below:

> 
>     def methodA(self):
>         "doc string"
>         objects = self.methodB(self)
> 	objects.reverse()
> 
> 	attrib = ''	
> 
> 	for object in objects:
> 		attrib = attrib + 'some html'
> 
> 	return attrib

def methodA(self):
  "doc string"
  objects = self.methodB(self)[:]
  objects.reverse()

Here, you're making a copy of what methodB returns, before doing stuff to it.

Otherwise, you can re-reverse what methodB returns using try: finally: in methodA.

If methodB is called by anything else, as methodB is recursive, you should either make it non-recursive, or access it via a methodC:

def methodC(self, object):
  return self.methodB(object)[:]

--
Steve Alexander
Software Engineer
Cat-Box limited
http://www.cat-box.net