Minor clean up of PEP 520.
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pep-0520.txt
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pep-0520.txt
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@ -16,8 +16,9 @@ Abstract
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This PEP changes the default class definition namespace to ``OrderedDict``.
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Furthermore, the order in which the attributes are defined in each class
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body will now be preserved in ``type.__definition_order__``. This allows
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introspection of the original definition order, e.g. by class decorators.
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body will now be preserved in the ``__definition_order__`` attribute of
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the class. This allows introspection of the original definition order,
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e.g. by class decorators.
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Note: just to be clear, this PEP is *not* about changing ``__dict__`` for
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classes to ``OrderedDict``.
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@ -62,9 +63,9 @@ Specification
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1. if ``__definition_order__`` is defined in the class body then the
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value is used as-is, though the attribute will still be read-only
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2. types that do not have a class definition (e.g. builtins) have
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2. classes that do not have a class definition (e.g. builtins) have
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their ``__definition_order__`` set to ``None``
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3. types for which `__prepare__()`` returned something other than
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3. classes for which `__prepare__()`` returned something other than
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``OrderedDict`` (or a subclass) have their ``__definition_order__``
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set to ``None`` (except where #1 applies)
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@ -78,8 +79,8 @@ The following code demonstrates roughly equivalent semantics::
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ham = None
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eggs = 5
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__definition_order__ = tuple(k for k in locals()
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if (!k.startswith('__') or
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!k.endswith('__')))
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if (not k.startswith('__') or
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not k.endswith('__')))
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Note that [pep487_] proposes a similar solution, albeit as part of a
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broader proposal.
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@ -169,14 +170,15 @@ The implementation is found in the tracker. [impl_]
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Alternatives
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============
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type.__dict__ as OrderedDict
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----------------------------
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<class>.__dict__ as OrderedDict
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-------------------------------
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Instead of storing the definition order in ``__definition_order__``,
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the now-ordered definition namespace could be copied into a new
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``OrderedDict``. This would mostly provide the same semantics.
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``OrderedDict``. This would then be used as the mapping proxied as
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``__dict__``. Doing so would mostly provide the same semantics.
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However, using ``OrderedDict`` for ``type,__dict__`` would obscure the
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However, using ``OrderedDict`` for ``__dict__`` would obscure the
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relationship with the definition namespace, making it less useful.
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Additionally, doing this would require significant changes to the
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semantics of the concrete ``dict`` C-API.
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