Minor clean up of PEP 520.

This commit is contained in:
Eric Snow 2016-06-07 20:09:27 -07:00
parent 06a5c815d7
commit 38a64f3338
1 changed files with 12 additions and 10 deletions

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@ -16,8 +16,9 @@ Abstract
This PEP changes the default class definition namespace to ``OrderedDict``.
Furthermore, the order in which the attributes are defined in each class
body will now be preserved in ``type.__definition_order__``. This allows
introspection of the original definition order, e.g. by class decorators.
body will now be preserved in the ``__definition_order__`` attribute of
the class. This allows introspection of the original definition order,
e.g. by class decorators.
Note: just to be clear, this PEP is *not* about changing ``__dict__`` for
classes to ``OrderedDict``.
@ -62,9 +63,9 @@ Specification
1. if ``__definition_order__`` is defined in the class body then the
value is used as-is, though the attribute will still be read-only
2. types that do not have a class definition (e.g. builtins) have
2. classes that do not have a class definition (e.g. builtins) have
their ``__definition_order__`` set to ``None``
3. types for which `__prepare__()`` returned something other than
3. classes for which `__prepare__()`` returned something other than
``OrderedDict`` (or a subclass) have their ``__definition_order__``
set to ``None`` (except where #1 applies)
@ -78,8 +79,8 @@ The following code demonstrates roughly equivalent semantics::
ham = None
eggs = 5
__definition_order__ = tuple(k for k in locals()
if (!k.startswith('__') or
!k.endswith('__')))
if (not k.startswith('__') or
not k.endswith('__')))
Note that [pep487_] proposes a similar solution, albeit as part of a
broader proposal.
@ -169,14 +170,15 @@ The implementation is found in the tracker. [impl_]
Alternatives
============
type.__dict__ as OrderedDict
----------------------------
<class>.__dict__ as OrderedDict
-------------------------------
Instead of storing the definition order in ``__definition_order__``,
the now-ordered definition namespace could be copied into a new
``OrderedDict``. This would mostly provide the same semantics.
``OrderedDict``. This would then be used as the mapping proxied as
``__dict__``. Doing so would mostly provide the same semantics.
However, using ``OrderedDict`` for ``type,__dict__`` would obscure the
However, using ``OrderedDict`` for ``__dict__`` would obscure the
relationship with the definition namespace, making it less useful.
Additionally, doing this would require significant changes to the
semantics of the concrete ``dict`` C-API.