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69 строки
1.7 KiB
ReStructuredText
69 строки
1.7 KiB
ReStructuredText
===============================================
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PEP487: Simpler customisation of class creation
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===============================================
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This is a backport of PEP487's simpler customisation of class
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creation by Martin Teichmann <https://www.python.org/dev/peps/pep-0487/>
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for Python versions before 3.6.
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PEP487 is free software: you can redistribute it and/or modify it
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under the terms of the GNU General Public License as published
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by the Free Software Foundation, either version 3 of the License,
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or (at your option) any later version.
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Subclass init
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=============
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>>> from pep487 import PEP487Object
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>>> class FooBase(PEP487Object):
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... foos = set()
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...
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... def __init_subclass__(cls, **kwargs):
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... cls.foos.add(cls.__name__)
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Using `PEP487Object` as base class all subclasses of FooBase
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will add their name to the common class variable 'foos'.
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>>> class Foo1(FooBase):
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... pass
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>>> class Foo2(FooBase):
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... pass
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Hence:
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>>> FooBase.foos
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{'Foo1', 'Foo2'}
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Property names and owner
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========================
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If a class object has a method `__set_name__` upon declaration
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of an PEP487Object class, it will be called:
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>>> class NamedProperty:
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... def __set_name__(self, owner, name):
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... self.context = owner
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... self.name = name
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>>> class Bar(PEP487Object):
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... foo = NamedProperty()
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... bar = NamedProperty()
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Consequently:
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>>> Bar.foo.name is 'foo' and Bar.foo.context is Bar
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True
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>>> Bar.bar.name is 'bar' and Bar.bar.context is Bar
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True
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Abstract base classes
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=====================
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Since `PEP487Object` has a custom metaclass, it is incompatible
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to `abc.ABC`. Therefore `pep487` contains patched versions of `ABC`
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and `ABCMeta`.
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