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import copy
import operator
class Empty:
def __str__(self):
return "EMPTY"
empty = Empty()
def new_method_proxy(func):
def inner(self, *args):
if self._wrapped is empty:
self._setup()
return func(self._wrapped, *args)
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.
"""
# Avoid infinite recursion when tracing __init__.
_wrapped = None
_kwargs = None
_django_override = False
def __init__(self):
# Note: if a subclass overrides __init__(), it will likely need to
# override __copy__() and __deepcopy__() as well.
self._wrapped = empty
__getattr__ = new_method_proxy(getattr)
def __setattr__(self, name, value):
if name in ["_wrapped", "_kwargs", "_warn_dynaconf_global_settings"]:
# Assign to __dict__ to avoid infinite __setattr__ loops.
self.__dict__[name] = value
else:
if self._wrapped is empty:
self._setup()
setattr(self._wrapped, name, value)
def __delattr__(self, name):
if name in ["_wrapped", "_kwargs"]:
raise TypeError(f"can't delete {name}.")
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):
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):
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
|
