[Python-Dev] bug or a feature? (original) (raw)

Terry Reedy tjreedy at udel.edu
Thu Jun 12 04:01:50 CEST 2008

"Maciej Fijalkowski" <fijall at gmail.com> wrote in message news:693bc9ab0806111759k14f7e672r1ebd20a85d4d5af5 at mail.gmail.com... | On Thu, Jun 12, 2008 at 2:32 AM, Terry Reedy <tjreedy at udel.edu> wrote: | > | > "Scott Dial" <scott+python-dev at scottdial.com> wrote in message | > news:4850263A.3040805 at scottdial.com... | > || If non-string keys are not allowed in dict, then the AddOns library | > | should be changed to add another dict to the object of interest to track | > | these AddOn instances. | > | > There are three possibilities with respect to dict and non-string keys. | > 1. All implementations must reject such. | > 2. Each implementation decides for itself. | > 3. All implementations must allow such. | > | > Current, CPython does not reject, eliminating 1). Since, as I understand | > it, at least 1 other implementation does reject, 3) is also eliminated | > until Guido decrees otherwise and such implementation(s) change. This | > leaves 2) as the de facto situation, but this could be made clearer in the | > docs: "The result of trying to add non-string keys to any dict | > attribute is implementation defined." This means that portable Python code | > must act as if 1) were the case. | > | > The Data Model chapter of the Reference Manual lists .dict as a special | > attribute of callables, modules, classes, and instances. It describes | > dict as a "namespace dictionary" or "implementation of the namespace" | > thereof. Since namespaces map names (or possibly non-name strings) to | > objects, this to me implies that an implementation is and should not be | > required to allow non-strings in dict. | > | > The same chapter has more than one sentence saying something like "o.x is | > equivalent to o.dict['x']". While one could read this as prohibiting | > o.dict[nonstring], one could also read it as being silent, neither | > allowing nor prohibiting. | > | > The builtin interface functions setattr, hasattr, getattr all require | > strings for accessing the underlying dict. Since they could have been | > defined otherwise, to accept any object as an attribute 'name' (key), this | _> again implies (to me) that dict_s are only intended and only required to | > have string keys. Hence, I was initially surprised that 1) above was not | > true. So I might add something stronger to the docs, something like "The | > special dict attributes are only intended to hold string keys. If an | > implementation allows other keys, that is only an current accidental | > side-effect of considerations of parsimony and efficiency." | > | > Contrariwise, if 3) were mandated, then I would think that the xxxattr | > functions should be changed.

| This is completely irrelevant. This post is not about assigning | non-string stuff to dict of class which works completely fine.

My apologies for clipping too much of Scott's post. Here is the rest that came before what I quoted, which makes clear, from first sentence to last line, that he is talking about assigning non-string stuff to dict of a class.

"The AddOns library uses class objects as keys in the dict, but that doesn't says anything about the usage of locals(). At no point in the AddOns library is locals() abused like this, so even if one asserts that assignment to the dict returned by locals() is a bug, the underlying behavior of interest is whether dict is allowed to have non-string keys.

from peak.util.addons import AddOn class C: pass class A(AddOn): pass spam = C() print spam.dict {} A(spam) print spam.dict {<class 'A'>: <A object at ...>} "

Whether non-strings keys in o.dict 'works fine' depends on one's definition of 'works fine'. In any case, as of 3.0a5, I thinks the docs could better clarify the status of this 'feature'. Whatever pronouncement Guido has made has not, that I could find, made it in.

| It's about abusing locals, which are not even given that they'll | modify this dict.

I thought it settled that that is a bad thing to do. Here the doc is pretty clear.

tjr

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