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137 lines
4.4 KiB
137 lines
4.4 KiB
from __future__ import annotations
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import copy
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import operator
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class Empty:
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def __str__(self):
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return "EMPTY"
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empty = Empty()
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def new_method_proxy(func):
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def inner(self, *args):
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if self._wrapped is empty:
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self._setup()
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return func(self._wrapped, *args)
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return inner
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class LazyObject:
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"""
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A wrapper for another class that can be used to delay instantiation of the
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wrapped class.
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By subclassing, you have the opportunity to intercept and alter the
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instantiation.
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"""
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# Avoid infinite recursion when tracing __init__.
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_wrapped = None
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_kwargs = None
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_django_override = False
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def __init__(self):
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# Note: if a subclass overrides __init__(), it will likely need to
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# override __copy__() and __deepcopy__() as well.
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self._wrapped = empty
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__getattr__ = new_method_proxy(getattr)
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def __setattr__(self, name, value):
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if name in ["_wrapped", "_kwargs", "_warn_dynaconf_global_settings"]:
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# Assign to __dict__ to avoid infinite __setattr__ loops.
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self.__dict__[name] = value
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else:
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if self._wrapped is empty:
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self._setup()
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setattr(self._wrapped, name, value)
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def __delattr__(self, name):
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if name in ["_wrapped", "_kwargs"]:
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raise TypeError(f"can't delete {name}.")
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if self._wrapped is empty:
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self._setup()
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delattr(self._wrapped, name)
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def _setup(self):
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"""
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Must be implemented by subclasses to initialize the wrapped object.
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"""
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raise NotImplementedError(
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"subclasses of LazyObject must provide a _setup() method"
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)
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# Because we have messed with __class__ below, we confuse pickle as to what
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# class we are pickling. We're going to have to initialize the wrapped
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# object to successfully pickle it, so we might as well just pickle the
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# wrapped object since they're supposed to act the same way.
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#
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# Unfortunately, if we try to simply act like the wrapped object, the ruse
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# will break down when pickle gets our id(). Thus we end up with pickle
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# thinking, in effect, that we are a distinct object from the wrapped
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# object, but with the same __dict__. This can cause problems (see #25389).
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#
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# So instead, we define our own __reduce__ method and custom unpickler. We
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# pickle the wrapped object as the unpickler's argument, so that pickle
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# will pickle it normally, and then the unpickler simply returns its
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# argument.
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def __reduce__(self):
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if self._wrapped is empty:
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self._setup()
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return (unpickle_lazyobject, (self._wrapped,))
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def __copy__(self):
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if self._wrapped is empty:
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# If uninitialized, copy the wrapper. Use type(self), not
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# self.__class__, because the latter is proxied.
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return type(self)()
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else:
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# If initialized, return a copy of the wrapped object.
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return copy.copy(self._wrapped)
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def __deepcopy__(self, memo):
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if self._wrapped is empty:
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# We have to use type(self), not self.__class__, because the
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# latter is proxied.
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result = type(self)()
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memo[id(self)] = result
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return result
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return copy.deepcopy(self._wrapped, memo)
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__bytes__ = new_method_proxy(bytes)
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__str__ = new_method_proxy(str)
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__bool__ = new_method_proxy(bool)
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# Introspection support
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__dir__ = new_method_proxy(dir)
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# Need to pretend to be the wrapped class, for the sake of objects that
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# care about this (especially in equality tests)
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__class__ = property(new_method_proxy(operator.attrgetter("__class__")))
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__eq__ = new_method_proxy(operator.eq)
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__lt__ = new_method_proxy(operator.lt)
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__gt__ = new_method_proxy(operator.gt)
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__ne__ = new_method_proxy(operator.ne)
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__hash__ = new_method_proxy(hash)
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# List/Tuple/Dictionary methods support
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__getitem__ = new_method_proxy(operator.getitem)
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__setitem__ = new_method_proxy(operator.setitem)
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__delitem__ = new_method_proxy(operator.delitem)
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__iter__ = new_method_proxy(iter)
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__len__ = new_method_proxy(len)
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__contains__ = new_method_proxy(operator.contains)
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def unpickle_lazyobject(wrapped):
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"""
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Used to unpickle lazy objects. Just return its argument, which will be the
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wrapped object.
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"""
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return wrapped
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