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116 lines
3.9 KiB
116 lines
3.9 KiB
# Custom property-like classes |
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from typing import Dict, Literal, MutableMapping, NewType, Optional, Sequence, Generic, TypeVar, Callable, Type, Any, Mapping, overload, Union |
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T = TypeVar('T') |
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O = TypeVar('O') |
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class CustomProperty(property, Generic[T]): |
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""" Subclass property for IDE support. |
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Subclasses need not call super().__init__(), |
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but might want to initialize self.property_name if such information is available """ |
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property_name: str = "<<name unknown>>" |
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def __init__(self): |
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# Overwrite property constructor |
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pass |
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def __set_name__(self, owner: Type[O], name: str): |
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""" Set name given in class body. |
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May not be called if assigned outside class definition """ |
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self.property_name = name |
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@overload # type: ignore |
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def __get__(self, obj: None, cls: Type[O]) -> 'CustomProperty[T]': ... |
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@overload |
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def __get__(self, obj: O, cls: Type[O]) -> T: ... |
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def __get__(self, obj: Optional[O], cls: Type[O]): |
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if obj is None: |
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return self |
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raise AttributeError(f"Cannot read property {self.property_name} of {obj:r}") |
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def __set__(self, obj: O, value: T): |
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raise AttributeError(f"Cannot write property {self.property_name} of {obj:r}") |
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def __delete__(self, obj: O): |
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raise AttributeError(f"Cannot delete property {self.property_name} of {obj:r}") |
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class CachedProperty(CustomProperty[T]): |
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""" A property that is only computed once per instance and then replaces |
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itself with an ordinary attribute. Deleting the attribute resets the |
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property. |
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Source: https://github.com/bottlepy/bottle/commit/fa7733e075da0d790d809aa3d2f53071897e6f76 |
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""" |
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def __init__(self, func: Callable[[O], T]): |
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self.__doc__ = getattr(func, '__doc__') |
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self.func = func |
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self.property_name = func.__name__ |
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def __get__(self, obj: Optional[O], cls: Type[O]): # type: ignore |
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if obj is None: |
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return self |
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value = obj.__dict__[self.property_name] = self.func(obj) |
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return value |
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class SettableCachedProperty(CachedProperty[T]): |
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def __set__(self, obj: O, value: T): |
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obj.__dict__[self.property_name] = value |
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class DictPathRoProperty(CustomProperty[T]): |
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_NoDefault = NewType("_NoDefault", object) |
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_nodefault = _NoDefault(object()) |
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def __init__(self, source_member: str, path: Sequence[str], |
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default: Union[T, _NoDefault]=_nodefault, type: Callable[[Any], T]=lambda x: x): |
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self.source_member = source_member |
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self.path = path |
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self.default = default |
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self.type = type |
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def _get_parent(self, obj: O, *, create=False) -> MutableMapping[str, Any]: |
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d: MutableMapping[str, Any] = getattr(obj, self.source_member) |
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for pc in self.path[:-1]: |
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try: |
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d = d[pc] |
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except KeyError: |
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if not create: |
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raise |
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nd: MutableMapping[str, Any] = {} |
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d[pc] = nd |
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d = nd |
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return d |
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def __get__(self, obj: Optional[O], cls: Type[O]): # type: ignore |
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if obj is None: |
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return self |
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try: |
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val = self._get_parent(obj)[self.path[-1]] |
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except KeyError: |
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if self.default is not self._nodefault: |
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return self.default |
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raise |
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else: |
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return self.type(val) |
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class DictPathProperty(DictPathRoProperty[T]): |
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def __init__(self, *args, allow_create_parents=True, **kwds): |
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super().__init__(*args, **kwds) |
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self.allow_create_parents = allow_create_parents |
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def __set__(self, obj, value): |
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self._get_parent(obj, create=self.allow_create_parents)[self.path[-1]] = value |
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def __delete__(self, obj): |
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del self._get_parent(obj)[self.path[-1]] |
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__all__ = ['CustomProperty', 'CachedProperty', 'SettableCachedProperty', 'DictPathRoProperty', 'DictPathProperty']
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