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82 lines
2.4 KiB
Python
82 lines
2.4 KiB
Python
from __future__ import annotations
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from collections.abc import Callable, Mapping
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from typing import Any, TypeVar, final, overload
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from ._exceptions import TypedAttributeLookupError
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T_Attr = TypeVar("T_Attr")
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T_Default = TypeVar("T_Default")
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undefined = object()
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def typed_attribute() -> Any:
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"""Return a unique object, used to mark typed attributes."""
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return object()
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class TypedAttributeSet:
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"""
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Superclass for typed attribute collections.
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Checks that every public attribute of every subclass has a type annotation.
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"""
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def __init_subclass__(cls) -> None:
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annotations: dict[str, Any] = getattr(cls, "__annotations__", {})
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for attrname in dir(cls):
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if not attrname.startswith("_") and attrname not in annotations:
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raise TypeError(
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f"Attribute {attrname!r} is missing its type annotation"
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)
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super().__init_subclass__()
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class TypedAttributeProvider:
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"""Base class for classes that wish to provide typed extra attributes."""
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@property
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def extra_attributes(self) -> Mapping[T_Attr, Callable[[], T_Attr]]:
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"""
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A mapping of the extra attributes to callables that return the corresponding
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values.
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If the provider wraps another provider, the attributes from that wrapper should
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also be included in the returned mapping (but the wrapper may override the
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callables from the wrapped instance).
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"""
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return {}
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@overload
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def extra(self, attribute: T_Attr) -> T_Attr: ...
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@overload
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def extra(self, attribute: T_Attr, default: T_Default) -> T_Attr | T_Default: ...
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@final
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def extra(self, attribute: Any, default: object = undefined) -> object:
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"""
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extra(attribute, default=undefined)
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Return the value of the given typed extra attribute.
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:param attribute: the attribute (member of a :class:`~TypedAttributeSet`) to
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look for
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:param default: the value that should be returned if no value is found for the
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attribute
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:raises ~anyio.TypedAttributeLookupError: if the search failed and no default
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value was given
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"""
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try:
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getter = self.extra_attributes[attribute]
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except KeyError:
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if default is undefined:
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raise TypedAttributeLookupError("Attribute not found") from None
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else:
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return default
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return getter()
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