67 lines
1.8 KiB
Python
67 lines
1.8 KiB
Python
"""
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meta.py
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Some useful metaclasses.
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"""
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class LeafClassesMeta(type):
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"""
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A metaclass for classes that keeps track of all of them that
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aren't base classes.
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>>> Parent = LeafClassesMeta('MyParentClass', (), {})
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>>> Parent in Parent._leaf_classes
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True
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>>> Child = LeafClassesMeta('MyChildClass', (Parent,), {})
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>>> Child in Parent._leaf_classes
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True
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>>> Parent in Parent._leaf_classes
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False
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>>> Other = LeafClassesMeta('OtherClass', (), {})
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>>> Parent in Other._leaf_classes
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False
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>>> len(Other._leaf_classes)
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1
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"""
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def __init__(cls, name, bases, attrs):
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if not hasattr(cls, '_leaf_classes'):
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cls._leaf_classes = set()
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leaf_classes = getattr(cls, '_leaf_classes')
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leaf_classes.add(cls)
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# remove any base classes
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leaf_classes -= set(bases)
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class TagRegistered(type):
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"""
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As classes of this metaclass are created, they keep a registry in the
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base class of all classes by a class attribute, indicated by attr_name.
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>>> FooObject = TagRegistered('FooObject', (), dict(tag='foo'))
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>>> FooObject._registry['foo'] is FooObject
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True
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>>> BarObject = TagRegistered('Barobject', (FooObject,), dict(tag='bar'))
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>>> FooObject._registry is BarObject._registry
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True
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>>> len(FooObject._registry)
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2
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'...' below should be 'jaraco.classes' but for pytest-dev/pytest#3396
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>>> FooObject._registry['bar']
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<class '....meta.Barobject'>
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"""
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attr_name = 'tag'
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def __init__(cls, name, bases, namespace):
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super(TagRegistered, cls).__init__(name, bases, namespace)
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if not hasattr(cls, '_registry'):
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cls._registry = {}
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meta = cls.__class__
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attr = getattr(cls, meta.attr_name, None)
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if attr:
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cls._registry[attr] = cls
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