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28 lines
1005 B
Python
28 lines
1005 B
Python
from abc import ABCMeta
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class AutoSlots(ABCMeta):
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"""
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Metaclass for automatically generating __slots__ based on superclass type annotations.
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Superclasses must set `__slots__ = ()` to make this work properly.
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This is a workaround for the fact that non-empty `__slots__` can't be used
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with multiple inheritance. Since we only use multiple inheritance with abstract
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classes, they can have empty `__slots__` and their attribute type annotations
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can be used to generate a full `__slots__` for the concrete class.
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"""
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def __new__(cls, name, bases, dctn):
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parents = set()
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for base in bases:
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parents |= set(base.mro())
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slots = tuple(dctn.get('__slots__', tuple()))
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for parent in parents:
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if not hasattr(parent, '__annotations__'):
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continue
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slots += tuple(getattr(parent, '__annotations__').keys())
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dctn['__slots__'] = slots
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return super().__new__(cls, name, bases, dctn)
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