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