[Twisted-Python] copy.deepcopy domish.Element works in python 2.5 but not in 2.6

Ralph Meijer twisted at ralphm.ik.nu
Fri Dec 18 08:37:36 EST 2009

On Thu, 2009-12-17 at 18:11 +0000, exarkun at twistedmatrix.com wrote:
> On 05:40 pm, gabriel.rossetti at arimaz.com wrote:
> >Hello everyone,
> >
> >for some reason copy.deepcopy forks great on a domish.Element on 2.5 
> >but
> >not in 2.6 :
> Actually, it looks like it works about equally well on either version. 
> While it looks like an exception was raised by deepcopy on Python 2.6, 
> notice that the exception was actually *ignored*.  You get back a copy, 
> and it even seems to have all the right attributes. ;)
> The infinite recursion in deepcopy happens on Python 2.5 as well.  I'm 
> not completely sure why it's not being reported, but it probably has to 
> do with tiny differences in how deepcopy works.  hasattr is well known 
> for swallowing exceptions silently.  The impressive thing is that the 
> error is reported at all in Python 2.6.
> A good rule of thumb is to assume that types don't support being copied 
> like this unless their docs explicitly state that they do.  If you want 
> this to be supported, it's probably not too hard to implement.  Feel 
> free to file a ticket with a patch. :)

There is an open ticket about this:


In short: it is probably a bad idea, and I'm curious about the possible
useful use cases.


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