Current File : //lib/python3/dist-packages/jaraco/classes/meta.py
"""
meta.py
Some useful metaclasses.
"""
class LeafClassesMeta(type):
"""
A metaclass for classes that keeps track of all of them that
aren't base classes.
>>> Parent = LeafClassesMeta('MyParentClass', (), {})
>>> Parent in Parent._leaf_classes
True
>>> Child = LeafClassesMeta('MyChildClass', (Parent,), {})
>>> Child in Parent._leaf_classes
True
>>> Parent in Parent._leaf_classes
False
>>> Other = LeafClassesMeta('OtherClass', (), {})
>>> Parent in Other._leaf_classes
False
>>> len(Other._leaf_classes)
1
"""
def __init__(cls, name, bases, attrs):
if not hasattr(cls, '_leaf_classes'):
cls._leaf_classes = set()
leaf_classes = getattr(cls, '_leaf_classes')
leaf_classes.add(cls)
# remove any base classes
leaf_classes -= set(bases)
class TagRegistered(type):
"""
As classes of this metaclass are created, they keep a registry in the
base class of all classes by a class attribute, indicated by attr_name.
>>> FooObject = TagRegistered('FooObject', (), dict(tag='foo'))
>>> FooObject._registry['foo'] is FooObject
True
>>> BarObject = TagRegistered('Barobject', (FooObject,), dict(tag='bar'))
>>> FooObject._registry is BarObject._registry
True
>>> len(FooObject._registry)
2
'...' below should be 'jaraco.classes' but for pytest-dev/pytest#3396
>>> FooObject._registry['bar']
<class '....meta.Barobject'>
"""
attr_name = 'tag'
def __init__(cls, name, bases, namespace):
super(TagRegistered, cls).__init__(name, bases, namespace)
if not hasattr(cls, '_registry'):
cls._registry = {}
meta = cls.__class__
attr = getattr(cls, meta.attr_name, None)
if attr:
cls._registry[attr] = cls
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