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219 lines (180 loc) · 7.51 KB
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# Copied from Django LazyObject
# https://github.com/django/django/blob/main/django/utils/functional.py
import copy
import operator
import typing as t
from .importer import import_from_string
empty = object()
def new_method_proxy(func):
def inner(self, *args):
if (_wrapped := self._wrapped) is empty:
self._setup()
_wrapped = self._wrapped
return func(_wrapped, *args)
inner._mask_wrapped = False
return inner
class LazyObject:
"""
A wrapper for another class that can be used to delay instantiation of the
wrapped class.
By subclassing, you have the opportunity to intercept and alter the
instantiation. If you don't need to do that, use SimpleLazyObject.
"""
# Avoid infinite recursion when tracing __init__ (#19456).
_wrapped = None
def __init__(self):
# Note: if a subclass overrides __init__(), it will likely need to
# override __copy__() and __deepcopy__() as well.
self._wrapped = empty
def __getattribute__(self, name):
if name == "_wrapped":
# Avoid recursion when getting wrapped object.
return super().__getattribute__(name)
value = super().__getattribute__(name)
# If attribute is a proxy method, raise an AttributeError to call
# __getattr__() and use the wrapped object method.
if not getattr(value, "_mask_wrapped", True):
raise AttributeError
return value
__getattr__ = new_method_proxy(getattr)
def __setattr__(self, name, value):
if name == "_wrapped":
# Assign to __dict__ to avoid infinite __setattr__ loops.
self.__dict__["_wrapped"] = value
else:
if self._wrapped is empty:
self._setup()
setattr(self._wrapped, name, value)
def __delattr__(self, name):
if name == "_wrapped":
raise TypeError("can't delete _wrapped.")
if self._wrapped is empty:
self._setup()
delattr(self._wrapped, name)
def _setup(self):
"""
Must be implemented by subclasses to initialize the wrapped object.
"""
raise NotImplementedError(
"subclasses of LazyObject must provide a _setup() method"
)
# Because we have messed with __class__ below, we confuse pickle as to what
# class we are pickling. We're going to have to initialize the wrapped
# object to successfully pickle it, so we might as well just pickle the
# wrapped object since they're supposed to act the same way.
#
# Unfortunately, if we try to simply act like the wrapped object, the ruse
# will break down when pickle gets our id(). Thus we end up with pickle
# thinking, in effect, that we are a distinct object from the wrapped
# object, but with the same __dict__. This can cause problems (see #25389).
#
# So instead, we define our own __reduce__ method and custom unpickler. We
# pickle the wrapped object as the unpickler's argument, so that pickle
# will pickle it normally, and then the unpickler simply returns its
# argument.
def __reduce__(self):
if self._wrapped is empty:
self._setup()
return (unpickle_lazyobject, (self._wrapped,))
def __copy__(self): # pragma: no cover
if self._wrapped is empty:
# If uninitialized, copy the wrapper. Use type(self), not
# self.__class__, because the latter is proxied.
return type(self)()
else:
# If initialized, return a copy of the wrapped object.
return copy.copy(self._wrapped)
def __deepcopy__(self, memo): # pragma: no cover
if self._wrapped is empty:
# We have to use type(self), not self.__class__, because the
# latter is proxied.
result = type(self)()
memo[id(self)] = result
return result
return copy.deepcopy(self._wrapped, memo)
__bytes__ = new_method_proxy(bytes)
__str__ = new_method_proxy(str)
__bool__ = new_method_proxy(bool)
# Introspection support
__dir__ = new_method_proxy(dir)
# Need to pretend to be the wrapped class, for the sake of objects that
# care about this (especially in equality tests)
__class__ = property(new_method_proxy(operator.attrgetter("__class__")))
__eq__ = new_method_proxy(operator.eq)
__lt__ = new_method_proxy(operator.lt)
__gt__ = new_method_proxy(operator.gt)
__ne__ = new_method_proxy(operator.ne)
__hash__ = new_method_proxy(hash)
# List/Tuple/Dictionary methods support
__getitem__ = new_method_proxy(operator.getitem)
__setitem__ = new_method_proxy(operator.setitem)
__delitem__ = new_method_proxy(operator.delitem)
__iter__ = new_method_proxy(iter)
__len__ = new_method_proxy(len)
__contains__ = new_method_proxy(operator.contains)
def unpickle_lazyobject(wrapped):
"""
Used to unpickle lazy objects. Just return its argument, which will be the
wrapped object.
"""
return wrapped
class SimpleLazyObject(LazyObject):
"""
A lazy object initialized from any function.
Designed for compound objects of unknown type. For builtins or objects of
known type, use django.utils.functional.lazy.
"""
def __init__(self, func: t.Callable) -> None:
"""
Pass in a callable that returns the object to be wrapped.
If copies are made of the resulting SimpleLazyObject, which can happen
in various circumstances within Django, then you must ensure that the
callable can be safely run more than once and will return the same
value.
"""
self.__dict__["_setupfunc"] = func
super().__init__()
def _setup(self) -> None:
self._wrapped = self._setupfunc()
# Return a meaningful representation of the lazy object for debugging
# without evaluating the wrapped object.
def __repr__(self) -> str:
if self._wrapped is empty:
repr_attr = self._setupfunc
else:
repr_attr = self._wrapped
return "<%s: %r>" % (type(self).__name__, repr_attr)
def __copy__(self) -> t.Any: # pragma: no cover
if self._wrapped is empty:
# If uninitialized, copy the wrapper. Use SimpleLazyObject, not
# self.__class__, because the latter is proxied.
return SimpleLazyObject(self._setupfunc)
else:
# If initialized, return a copy of the wrapped object.
return copy.copy(self._wrapped)
def __deepcopy__(self, memo: t.Any) -> t.Any: # pragma: no cover
if self._wrapped is empty:
# We have to use SimpleLazyObject, not self.__class__, because the
# latter is proxied.
result = SimpleLazyObject(self._setupfunc)
memo[id(self)] = result
return result
return copy.deepcopy(self._wrapped, memo)
__add__ = new_method_proxy(operator.add)
@new_method_proxy
def __radd__(self, other: t.Any) -> t.Any:
return other + self
class LazyStrImport(LazyObject):
def __init__(self, import_str: str):
self.__dict__["_import_str"] = import_str
super(LazyStrImport, self).__init__()
@t.no_type_check
def _setup(self):
if self._wrapped is empty:
self._wrapped = import_from_string(self._import_str)
return self._wrapped
@t.no_type_check
def __call__(self, *args: t.Any, **kwargs: t.Any) -> t.Any:
if self._wrapped is empty:
self._setup()
return self._wrapped(*args, **kwargs)