[Python-ideas] Being able to specify "copy mode" to copy.deepcopy

Vitor Bosshard algorias at gmail.com
Tue Dec 15 17:19:43 CET 2009

2009/12/15 Ram Rachum <cool-rr at cool-rr.com>:
> MRAB <python at ...> writes:
>> cool-RR wrote:
>> > What do you think?
>> >
>> My own feeling is that this is a misuse of __deepcopy__: if you ask for
>> a copy (of a mutable object) then you should get a copy (for immutable
>> objects copying isn't necessary).
> I agree it that the Persistent.__deecopy__ thing does smell like misuse on my
> part. However I'd be happy to hear any alternative suggestion you have on how
> to solve the problem I have.

Deepcopy is a very simple operation conceptually, there's no need to
make it more complicated. How about implementing __deepcopy__ in your
world state objects? Specify attributes that don't need copying. You
can even use the Persistent class to signal that. Something like this

def __deepcopy__(self):
  new = self.__class__()
  for k,v in self.__dict__.iteritems():
    setattr(new, k, v if isinstance(v, Persistent) else deepcopy(v))
  return new


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