On 2012-06-18, at 1:35 PM, PJ Eby wrote:
> On Fri, Jun 15, 2012 at 5:03 PM, R. David Murray <[email protected]>
> wrote:
> On Fri, 15 Jun 2012 22:48:42 +0200, Victor Stinner <[email protected]>
> wrote:
> > > 1. Should we keep 'Parameter.implemented' or not. *Please vote*
>
> -1 to implemented.
>
> > I still disagree with the deepcopy. I read somewhere that Python
> > developers are consenting adult. If someone really want to modify a
> > Signature, it would be nice to provide a simple method to copy it. But
> > I don't see why it should be copied *by default*. I expect that
> > modifying a signature is more rare than just reading a signature.
>
> The issue isn't "consenting adults", the issue is consistency.
> Without the deepcopy, sometimes what you get back from the
> inspect function is freely modifiable and sometimes it is not.
> That inconsistency is a bad thing.
>
> Then just copy the signature itself; as currently written, this is going to
> copy the annotation objects, which could produce weird side-effects from
> introspection. Using deepcopy seems like overkill when all that's needed is
> a new Signature instance with a fresh OrderedDict.
That's an excerpt from Signature.__deepcopy__:
cls = type(self)
sig = cls.__new__(cls)
sig.parameters = OrderedDict((name, param.__copy__()) \
for name, param in self.parameters.items())
And Parameter.__copy__:
cls = type(self)
copy = cls.__new__(cls)
copy.__dict__.update(self.__dict__)
return copy
So we don't recursively deepcopy parameters in Signature.__deepcopy__
(I hope that we don't violate the deepcopy meaning here)
> Or, better yet: make signature and parameter objects immutable (along with
> the OrderedDict) and the whole problem of modification and copying goes away
> altogether. Or is there some reason not mentioned in the PEP why mutability
> is necessary? (The PEP provides no rationale at present for making any part
> of a signature mutable)
The rationale is that sometimes you need to modify signatures.
For instance, in decorators.
-
Yury
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