Viewing file:  _utilities.py (2.79 KB) -rw-r--r--
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from __future__ import annotations
import typing as t
from weakref import ref
from blinker._saferef import BoundMethodWeakref
IdentityType = t.Union[t.Tuple[int, int], str, int]
class _symbol:
def __init__(self, name):
"""Construct a new named symbol."""
self.__name__ = self.name = name
def __reduce__(self):
return symbol, (self.name,)
def __repr__(self):
return self.name
_symbol.__name__ = "symbol"
class symbol:
"""A constant symbol.
>>> symbol('foo') is symbol('foo')
True
>>> symbol('foo')
foo
A slight refinement of the MAGICCOOKIE=object() pattern. The primary
advantage of symbol() is its repr(). They are also singletons.
Repeated calls of symbol('name') will all return the same instance.
"""
symbols = {} # type: ignore[var-annotated]
def __new__(cls, name):
try:
return cls.symbols[name]
except KeyError:
return cls.symbols.setdefault(name, _symbol(name))
def hashable_identity(obj: object) -> IdentityType:
if hasattr(obj, "__func__"):
return (id(obj.__func__), id(obj.__self__)) # type: ignore[attr-defined]
elif hasattr(obj, "im_func"):
return (id(obj.im_func), id(obj.im_self)) # type: ignore[attr-defined]
elif isinstance(obj, (int, str)):
return obj
else:
return id(obj)
WeakTypes = (ref, BoundMethodWeakref)
class annotatable_weakref(ref):
"""A weakref.ref that supports custom instance attributes."""
receiver_id: t.Optional[IdentityType]
sender_id: t.Optional[IdentityType]
def reference( # type: ignore[no-untyped-def]
object, callback=None, **annotations
) -> annotatable_weakref:
"""Return an annotated weak ref."""
if callable(object):
weak = callable_reference(object, callback)
else:
weak = annotatable_weakref(object, callback)
for key, value in annotations.items():
setattr(weak, key, value)
return weak # type: ignore[no-any-return]
def callable_reference(object, callback=None):
"""Return an annotated weak ref, supporting bound instance methods."""
if hasattr(object, "im_self") and object.im_self is not None:
return BoundMethodWeakref(target=object, on_delete=callback)
elif hasattr(object, "__self__") and object.__self__ is not None:
return BoundMethodWeakref(target=object, on_delete=callback)
return annotatable_weakref(object, callback)
class lazy_property:
"""A @property that is only evaluated once."""
def __init__(self, deferred):
self._deferred = deferred
self.__doc__ = deferred.__doc__
def __get__(self, obj, cls):
if obj is None:
return self
value = self._deferred(obj)
setattr(obj, self._deferred.__name__, value)
return value
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