[Python-Dev] bug or a feature?
Terry Reedy
tjreedy at udel.edu
Thu Jun 12 21:38:09 CEST 2008
"Phillip J. Eby" <pje at telecommunity.com> wrote in message
news:20080612100048.7EEEA3A405F at sparrow.telecommunity.com...
| At 08:32 PM 6/11/2008 -0400, Terry Reedy wrote:
| >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__[non_string], one could also read it as being silent, neither
| >allowing nor prohibiting.
|
| As it happens, most objects' __dict__ slots are settable by default,
| and *require* that you set it to a dict or subclass thereof. This
| seems (to me) to imply that a standard dictionary (i.e. one
| supporting keys of any type) is required. (In the sense that a dict
| subclass which rejects non-strings would be violating the Liskov
principle.)
Is this requirement a documented Python requirement (not that I found), an
undocumented Python requirement, or a CPython-specific requirement (that
other implementations may freely ignore)?
I don't have much opinion on what the rules for __dict__ attributes should
be, just that whatever they are should be documented. This include
implementation-defined aspects. This will help both implementors and users
who wish to write Python code rather that CPython code.
If there is a consensus and BDFL pronouncement, I will make or help review
suggested doc changes.
tjr
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