291 lines
10 KiB
Python
291 lines
10 KiB
Python
import operator
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from functools import wraps, update_wrapper
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# You can't trivially replace this `functools.partial` because this binds to
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# classes and returns bound instances, whereas functools.partial (on CPython)
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# 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), **dict(kwargs, **morekwargs))
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return _curried
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def memoize(func, cache, num_args):
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"""
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Wrap a function so that results for any argument tuple are stored in
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'cache'. Note that the args to the function must be usable as dictionary
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keys.
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Only the first num_args are considered when creating the key.
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"""
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@wraps(func)
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def wrapper(*args):
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mem_args = args[:num_args]
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if mem_args in cache:
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return cache[mem_args]
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result = func(*args)
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cache[mem_args] = result
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return result
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return wrapper
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class Promise(object):
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"""
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This is just a base class for the proxy class created in
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the closure of the lazy function. It can be used to recognize
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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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Turns any callable into a lazy evaluated callable. You need to give result
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classes or types -- 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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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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__dispatch = None
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def __init__(self, args, kw):
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self.__func = func
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self.__args = args
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self.__kw = kw
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if self.__dispatch is None:
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self.__prepare_class__()
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def __reduce__(self):
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return (
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_lazy_proxy_unpickle,
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(self.__func, self.__args, self.__kw) + resultclasses
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)
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def __prepare_class__(cls):
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cls.__dispatch = {}
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for resultclass in resultclasses:
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cls.__dispatch[resultclass] = {}
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for type_ in reversed(resultclass.mro()):
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for (k, v) in type_.__dict__.items():
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# All __promise__ return the same wrapper method, but they
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# also do setup, inserting the method into the dispatch
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# dict.
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meth = cls.__promise__(resultclass, k, v)
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if hasattr(cls, k):
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continue
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setattr(cls, k, meth)
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cls._delegate_str = str in resultclasses
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cls._delegate_unicode = unicode in resultclasses
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assert not (cls._delegate_str and cls._delegate_unicode), "Cannot call lazy() with both str and unicode return types."
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if cls._delegate_unicode:
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cls.__unicode__ = cls.__unicode_cast
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elif cls._delegate_str:
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cls.__str__ = cls.__str_cast
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__prepare_class__ = classmethod(__prepare_class__)
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def __promise__(cls, klass, funcname, func):
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# Builds a wrapper around some magic method and registers that magic
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# method for the given type and method name.
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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 = self.__func(*self.__args, **self.__kw)
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for t in type(res).mro():
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if t in self.__dispatch:
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return self.__dispatch[t][funcname](res, *args, **kw)
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raise TypeError("Lazy object returned unexpected type.")
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if klass not in cls.__dispatch:
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cls.__dispatch[klass] = {}
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cls.__dispatch[klass][funcname] = func
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return __wrapper__
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__promise__ = classmethod(__promise__)
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def __unicode_cast(self):
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return self.__func(*self.__args, **self.__kw)
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def __str_cast(self):
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return str(self.__func(*self.__args, **self.__kw))
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def __cmp__(self, rhs):
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if self._delegate_str:
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s = str(self.__func(*self.__args, **self.__kw))
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elif self._delegate_unicode:
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s = unicode(self.__func(*self.__args, **self.__kw))
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else:
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s = self.__func(*self.__args, **self.__kw)
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if isinstance(rhs, Promise):
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return -cmp(rhs, s)
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else:
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return cmp(s, rhs)
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def __mod__(self, rhs):
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if self._delegate_str:
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return str(self) % rhs
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elif self._delegate_unicode:
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return unicode(self) % rhs
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else:
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raise AssertionError('__mod__ not supported for non-string types')
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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 allow_lazy(func, *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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@wraps(func)
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def wrapper(*args, **kwargs):
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for arg in list(args) + kwargs.values():
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if isinstance(arg, Promise):
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break
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else:
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return func(*args, **kwargs)
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return lazy(func, *resultclasses)(*args, **kwargs)
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return wrapper
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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(object):
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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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def __init__(self):
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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 initialise the wrapped object.
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"""
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raise NotImplementedError
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# introspection support:
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__members__ = property(lambda self: self.__dir__())
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__dir__ = new_method_proxy(dir)
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class SimpleLazyObject(LazyObject):
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"""
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A lazy object initialised 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(SimpleLazyObject, self).__init__()
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def _setup(self):
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self._wrapped = self._setupfunc()
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__str__ = new_method_proxy(str)
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__unicode__ = new_method_proxy(unicode)
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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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else:
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import copy
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return copy.deepcopy(self._wrapped, memo)
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# Need to pretend to be the wrapped class, for the sake of objects that care
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# 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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__hash__ = new_method_proxy(hash)
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__nonzero__ = new_method_proxy(bool)
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class lazy_property(property):
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"""
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A property that works with subclasses by wrapping the decorated
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functions of the base class.
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"""
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def __new__(cls, fget=None, fset=None, fdel=None, doc=None):
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if fget is not None:
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@wraps(fget)
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def fget(instance, instance_type=None, name=fget.__name__):
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return getattr(instance, name)()
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if fset is not None:
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@wraps(fset)
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def fset(instance, value, name=fset.__name__):
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return getattr(instance, name)(value)
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if fdel is not None:
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@wraps(fdel)
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def fdel(instance, name=fdel.__name__):
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return getattr(instance, name)()
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return property(fget, fset, fdel, doc)
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def partition(predicate, values):
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"""
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Splits 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 > 3, range(5))
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[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 |