Source code for django.utils.functional

import copy
import operator
import sys
from functools import wraps

from django.utils import six
from django.utils.six.moves import copyreg

# You can't trivially replace this with `functools.partial` because this binds
# to classes and returns bound instances, whereas functools.partial (on
# CPython) is a type and its instances don't bind.
def curry(_curried_func, *args, **kwargs):
    def _curried(*moreargs, **morekwargs):
        return _curried_func(*(args + moreargs), **dict(kwargs, **morekwargs))
    return _curried

[docs]class cached_property(object): """ Decorator that converts a method with a single self argument into a property cached on the instance. Optional ``name`` argument allows you to make cached properties of other methods. (e.g. url = cached_property(get_absolute_url, name='url') ) """ def __init__(self, func, name=None): self.func = func self.__doc__ = getattr(func, '__doc__') = name or func.__name__ def __get__(self, instance, type=None): if instance is None: return self res = instance.__dict__[] = self.func(instance) return res
class Promise(object): """ This is just a base class for the proxy class created in the closure of the lazy function. It can be used to recognize promises in code. """ pass def lazy(func, *resultclasses): """ Turns any callable into a lazy evaluated callable. You need to give result classes or types -- at least one is needed so that the automatic forcing of the lazy evaluation code is triggered. Results are not memoized; the function is evaluated on every access. """ @total_ordering class __proxy__(Promise): """ Encapsulate a function call and act as a proxy for methods that are called on the result of that function. The function is not evaluated until one of the methods on the result is called. """ __prepared = False def __init__(self, args, kw): self.__args = args self.__kw = kw if not self.__prepared: self.__prepare_class__() self.__prepared = True def __reduce__(self): return ( _lazy_proxy_unpickle, (func, self.__args, self.__kw) + resultclasses ) @classmethod def __prepare_class__(cls): for resultclass in resultclasses: for type_ in resultclass.mro(): for method_name in type_.__dict__.keys(): # All __promise__ return the same wrapper method, they # look up the correct implementation when called. if hasattr(cls, method_name): continue meth = cls.__promise__(method_name) setattr(cls, method_name, meth) cls._delegate_bytes = bytes in resultclasses cls._delegate_text = six.text_type in resultclasses assert not (cls._delegate_bytes and cls._delegate_text), ( "Cannot call lazy() with both bytes and text return types.") if cls._delegate_text: if six.PY3: cls.__str__ = cls.__text_cast else: cls.__unicode__ = cls.__text_cast cls.__str__ = cls.__bytes_cast_encoded elif cls._delegate_bytes: if six.PY3: cls.__bytes__ = cls.__bytes_cast else: cls.__str__ = cls.__bytes_cast @classmethod def __promise__(cls, method_name): # Builds a wrapper around some magic method def __wrapper__(self, *args, **kw): # Automatically triggers the evaluation of a lazy value and # applies the given magic method of the result type. res = func(*self.__args, **self.__kw) return getattr(res, method_name)(*args, **kw) return __wrapper__ def __text_cast(self): return func(*self.__args, **self.__kw) def __bytes_cast(self): return bytes(func(*self.__args, **self.__kw)) def __bytes_cast_encoded(self): return func(*self.__args, **self.__kw).encode('utf-8') def __cast(self): if self._delegate_bytes: return self.__bytes_cast() elif self._delegate_text: return self.__text_cast() else: return func(*self.__args, **self.__kw) def __ne__(self, other): if isinstance(other, Promise): other = other.__cast() return self.__cast() != other def __eq__(self, other): if isinstance(other, Promise): other = other.__cast() return self.__cast() == other def __lt__(self, other): if isinstance(other, Promise): other = other.__cast() return self.__cast() < other def __hash__(self): return hash(self.__cast()) def __mod__(self, rhs): if self._delegate_bytes and six.PY2: return bytes(self) % rhs elif self._delegate_text: return six.text_type(self) % rhs return self.__cast() % rhs def __deepcopy__(self, memo): # Instances of this class are effectively immutable. It's just a # collection of functions. So we don't need to do anything # complicated for copying. memo[id(self)] = self return self @wraps(func) def __wrapper__(*args, **kw): # Creates the proxy object, instead of the actual value. return __proxy__(args, kw) return __wrapper__ def _lazy_proxy_unpickle(func, args, kwargs, *resultclasses): return lazy(func, *resultclasses)(*args, **kwargs)
[docs]def allow_lazy(func, *resultclasses): """ A decorator that allows a function to be called with one or more lazy arguments. If none of the args are lazy, the function is evaluated immediately, otherwise a __proxy__ is returned that will evaluate the function when needed. """ lazy_func = lazy(func, *resultclasses) @wraps(func) def wrapper(*args, **kwargs): for arg in list(args) + list(six.itervalues(kwargs)): if isinstance(arg, Promise): break else: return func(*args, **kwargs) return lazy_func(*args, **kwargs) return wrapper
empty = object() 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(object): """ 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): self._wrapped = empty __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. It also appears to stop __reduce__ from being # called. So, we define __getstate__ in a way that cooperates with the way # that pickle interprets this class. This fails when the wrapped class is # a builtin, but it is better than nothing. def __getstate__(self): if self._wrapped is empty: self._setup() return self._wrapped.__dict__ # Python 3.3 will call __reduce__ when pickling; this method is needed # to serialize and deserialize correctly. @classmethod def __newobj__(cls, *args): return cls.__new__(cls, *args) def __reduce_ex__(self, proto): if proto >= 2: # On Py3, since the default protocol is 3, pickle uses the # ``__newobj__`` method (& more efficient opcodes) for writing. return (self.__newobj__, (self.__class__,), self.__getstate__()) else: # On Py2, the default protocol is 0 (for back-compat) & the above # code fails miserably (see regression test). Instead, we return # exactly what's returned if there's no ``__reduce__`` method at # all. return (copyreg._reconstructor, (self.__class__, object, None), self.__getstate__()) 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) if six.PY3: __bytes__ = new_method_proxy(bytes) __str__ = new_method_proxy(str) __bool__ = new_method_proxy(bool) else: __str__ = new_method_proxy(str) __unicode__ = new_method_proxy(unicode) __nonzero__ = 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) __ne__ = new_method_proxy( __hash__ = new_method_proxy(hash) # Dictionary methods support __getitem__ = new_method_proxy(operator.getitem) __setitem__ = new_method_proxy(operator.setitem) __delitem__ = new_method_proxy(operator.delitem) __len__ = new_method_proxy(len) __contains__ = new_method_proxy(operator.contains) # Workaround for _super = super 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): """ 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(SimpleLazyObject, self).__init__() def _setup(self): self._wrapped = self._setupfunc() # Return a meaningful representation of the lazy object for debugging # without evaluating the wrapped object. def __repr__(self): if self._wrapped is empty: repr_attr = self._setupfunc else: repr_attr = self._wrapped return '<%s: %r>' % (type(self).__name__, repr_attr) def __deepcopy__(self, memo): 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) class lazy_property(property): """ A property that works with subclasses by wrapping the decorated functions of the base class. """ def __new__(cls, fget=None, fset=None, fdel=None, doc=None): if fget is not None: @wraps(fget) def fget(instance, instance_type=None, name=fget.__name__): return getattr(instance, name)() if fset is not None: @wraps(fset) def fset(instance, value, name=fset.__name__): return getattr(instance, name)(value) if fdel is not None: @wraps(fdel) def fdel(instance, name=fdel.__name__): return getattr(instance, name)() return property(fget, fset, fdel, doc) def partition(predicate, values): """ Splits the values into two sets, based on the return value of the function (True/False). e.g.: >>> partition(lambda x: x > 3, range(5)) [0, 1, 2, 3], [4] """ results = ([], []) for item in values: results[predicate(item)].append(item) return results if sys.version_info >= (2, 7, 2): from functools import total_ordering else: # For Python < 2.7.2. total_ordering in versions prior to 2.7.2 is buggy. # See for details. For these versions use # code borrowed from Python 2.7.3. def total_ordering(cls): """Class decorator that fills in missing ordering methods""" convert = { '__lt__': [('__gt__', lambda self, other: not (self < other or self == other)), ('__le__', lambda self, other: self < other or self == other), ('__ge__', lambda self, other: not self < other)], '__le__': [('__ge__', lambda self, other: not self <= other or self == other), ('__lt__', lambda self, other: self <= other and not self == other), ('__gt__', lambda self, other: not self <= other)], '__gt__': [('__lt__', lambda self, other: not (self > other or self == other)), ('__ge__', lambda self, other: self > other or self == other), ('__le__', lambda self, other: not self > other)], '__ge__': [('__le__', lambda self, other: (not self >= other) or self == other), ('__gt__', lambda self, other: self >= other and not self == other), ('__lt__', lambda self, other: not self >= other)] } roots = set(dir(cls)) & set(convert) if not roots: raise ValueError('must define at least one ordering operation: < > <= >=') root = max(roots) # prefer __lt__ to __le__ to __gt__ to __ge__ for opname, opfunc in convert[root]: if opname not in roots: opfunc.__name__ = opname opfunc.__doc__ = getattr(int, opname).__doc__ setattr(cls, opname, opfunc) return cls