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

[Steve Alexander]

Erik Enge wrote:

> On Mon, 26 Feb 2001, Steve Alexander wrote:
> 
> 
>> Chris McDonough wrote:
>> 
>> 
>>> The use of a literal anonymous list in methodb's signature for "objects" may
>>> have something to do with the results you're getting on conflict.  Try
>>> assigning "objects" to an empty list in the method body instead.
>> 
>> Of course!
> 
> 
> I'm missing out on something here.  Why is this an "of course"?  What's a
> "literal anonymous list"?

Consider this method:

   def methodFoo(self, objects=[]):
     # do stuff, including altering the list objects

The list that is assigned to "objects" in the definition of arguments is 
only created once. There is only one instance of the list for all the 
calls to methodFoo. If you alter that list, then it is altered for the 
future too.

Try it in Python from the interactive prompt:

 >>> def foo(o=[]):
...   o.append('x')
...   print o
...
 >>> foo()
['x']
 >>> foo()
['x', 'x']
 >>> foo()
['x', 'x', 'x']
 >>>

--
Steve Alexander
Software Engineer
Cat-Box limited