389 lines
13 KiB
Python
389 lines
13 KiB
Python
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import copy
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import itertools
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import operator
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from functools import total_ordering, wraps
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# You can't trivially replace this with `functools.partial` because this binds
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# to classes and returns bound instances, whereas functools.partial (on
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# CPython) is a type and its instances don't bind.
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def curry(_curried_func, *args, **kwargs):
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def _curried(*moreargs, **morekwargs):
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return _curried_func(*args, *moreargs, **{**kwargs, **morekwargs})
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return _curried
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class cached_property:
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"""
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Decorator that converts a method with a single self argument into a
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property cached on the instance.
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Optional ``name`` argument allows you to make cached properties of other
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methods. (e.g. url = cached_property(get_absolute_url, name='url') )
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"""
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def __init__(self, func, name=None):
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self.func = func
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self.__doc__ = getattr(func, '__doc__')
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self.name = name or func.__name__
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def __get__(self, instance, cls=None):
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"""
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Call the function and put the return value in instance.__dict__ so that
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subsequent attribute access on the instance returns the cached value
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instead of calling cached_property.__get__().
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"""
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if instance is None:
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return self
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res = instance.__dict__[self.name] = self.func(instance)
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return res
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class Promise:
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"""
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Base class for the proxy class created in the closure of the lazy function.
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It's used to recognize promises in code.
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"""
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pass
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def lazy(func, *resultclasses):
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"""
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Turn any callable into a lazy evaluated callable. result classes or types
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is required -- at least one is needed so that the automatic forcing of
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the lazy evaluation code is triggered. Results are not memoized; the
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function is evaluated on every access.
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"""
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@total_ordering
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class __proxy__(Promise):
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"""
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Encapsulate a function call and act as a proxy for methods that are
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called on the result of that function. The function is not evaluated
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until one of the methods on the result is called.
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"""
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__prepared = False
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def __init__(self, args, kw):
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self.__args = args
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self.__kw = kw
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if not self.__prepared:
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self.__prepare_class__()
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self.__prepared = True
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def __reduce__(self):
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return (
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_lazy_proxy_unpickle,
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(func, self.__args, self.__kw) + resultclasses
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)
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def __repr__(self):
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return repr(self.__cast())
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@classmethod
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def __prepare_class__(cls):
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for resultclass in resultclasses:
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for type_ in resultclass.mro():
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for method_name in type_.__dict__:
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# All __promise__ return the same wrapper method, they
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# look up the correct implementation when called.
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if hasattr(cls, method_name):
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continue
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meth = cls.__promise__(method_name)
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setattr(cls, method_name, meth)
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cls._delegate_bytes = bytes in resultclasses
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cls._delegate_text = str in resultclasses
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assert not (cls._delegate_bytes and cls._delegate_text), (
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"Cannot call lazy() with both bytes and text return types.")
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if cls._delegate_text:
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cls.__str__ = cls.__text_cast
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elif cls._delegate_bytes:
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cls.__bytes__ = cls.__bytes_cast
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@classmethod
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def __promise__(cls, method_name):
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# Builds a wrapper around some magic method
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def __wrapper__(self, *args, **kw):
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# Automatically triggers the evaluation of a lazy value and
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# applies the given magic method of the result type.
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res = func(*self.__args, **self.__kw)
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return getattr(res, method_name)(*args, **kw)
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return __wrapper__
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def __text_cast(self):
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return func(*self.__args, **self.__kw)
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def __bytes_cast(self):
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return bytes(func(*self.__args, **self.__kw))
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def __bytes_cast_encoded(self):
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return func(*self.__args, **self.__kw).encode()
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def __cast(self):
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if self._delegate_bytes:
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return self.__bytes_cast()
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elif self._delegate_text:
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return self.__text_cast()
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else:
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return func(*self.__args, **self.__kw)
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def __str__(self):
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# object defines __str__(), so __prepare_class__() won't overload
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# a __str__() method from the proxied class.
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return str(self.__cast())
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def __eq__(self, other):
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if isinstance(other, Promise):
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other = other.__cast()
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return self.__cast() == other
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def __lt__(self, other):
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if isinstance(other, Promise):
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other = other.__cast()
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return self.__cast() < other
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def __hash__(self):
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return hash(self.__cast())
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def __mod__(self, rhs):
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if self._delegate_text:
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return str(self) % rhs
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return self.__cast() % rhs
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def __deepcopy__(self, memo):
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# Instances of this class are effectively immutable. It's just a
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# collection of functions. So we don't need to do anything
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# complicated for copying.
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memo[id(self)] = self
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return self
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@wraps(func)
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def __wrapper__(*args, **kw):
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# Creates the proxy object, instead of the actual value.
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return __proxy__(args, kw)
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return __wrapper__
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def _lazy_proxy_unpickle(func, args, kwargs, *resultclasses):
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return lazy(func, *resultclasses)(*args, **kwargs)
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def lazystr(text):
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"""
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Shortcut for the common case of a lazy callable that returns str.
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"""
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return lazy(str, str)(text)
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def keep_lazy(*resultclasses):
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"""
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A decorator that allows a function to be called with one or more lazy
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arguments. If none of the args are lazy, the function is evaluated
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immediately, otherwise a __proxy__ is returned that will evaluate the
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function when needed.
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"""
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if not resultclasses:
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raise TypeError("You must pass at least one argument to keep_lazy().")
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def decorator(func):
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lazy_func = lazy(func, *resultclasses)
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@wraps(func)
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def wrapper(*args, **kwargs):
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if any(isinstance(arg, Promise) for arg in itertools.chain(args, kwargs.values())):
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return lazy_func(*args, **kwargs)
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return func(*args, **kwargs)
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return wrapper
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return decorator
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def keep_lazy_text(func):
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"""
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A decorator for functions that accept lazy arguments and return text.
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"""
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return keep_lazy(str)(func)
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empty = object()
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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. If you don't need to do that, use SimpleLazyObject.
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"""
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# Avoid infinite recursion when tracing __init__ (#19456).
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_wrapped = None
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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 == "_wrapped":
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# Assign to __dict__ to avoid infinite __setattr__ loops.
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self.__dict__["_wrapped"] = 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 == "_wrapped":
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raise TypeError("can't delete _wrapped.")
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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('subclasses of LazyObject must provide a _setup() method')
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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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__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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class SimpleLazyObject(LazyObject):
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"""
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A lazy object initialized from any function.
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Designed for compound objects of unknown type. For builtins or objects of
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known type, use django.utils.functional.lazy.
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"""
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def __init__(self, func):
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"""
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Pass in a callable that returns the object to be wrapped.
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If copies are made of the resulting SimpleLazyObject, which can happen
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in various circumstances within Django, then you must ensure that the
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callable can be safely run more than once and will return the same
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value.
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"""
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self.__dict__['_setupfunc'] = func
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super().__init__()
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def _setup(self):
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self._wrapped = self._setupfunc()
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# Return a meaningful representation of the lazy object for debugging
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# without evaluating the wrapped object.
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def __repr__(self):
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if self._wrapped is empty:
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repr_attr = self._setupfunc
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else:
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repr_attr = self._wrapped
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return '<%s: %r>' % (type(self).__name__, repr_attr)
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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 SimpleLazyObject, not
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# self.__class__, because the latter is proxied.
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return SimpleLazyObject(self._setupfunc)
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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 SimpleLazyObject, not self.__class__, because the
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# latter is proxied.
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result = SimpleLazyObject(self._setupfunc)
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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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def partition(predicate, values):
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"""
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Split the values into two sets, based on the return value of the function
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(True/False). e.g.:
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>>> partition(lambda x: x > 3, range(5))
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[0, 1, 2, 3], [4]
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"""
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results = ([], [])
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for item in values:
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results[predicate(item)].append(item)
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return results
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