Python 有没有办法通过collections.namedtuple支持weakrefs?
我想对namedtuple使用弱引用,但失败了:Python 有没有办法通过collections.namedtuple支持weakrefs?,python,python-2.7,weak-references,Python,Python 2.7,Weak References,我想对namedtuple使用弱引用,但失败了: >>> import collections >>> import weakref >>> >>> Foo = collections.namedtuple('Foo','a b c') >>> weakref.ref(Foo(1,2,3)) Traceback (most recent call last): File "<stdin>",
>>> import collections
>>> import weakref
>>>
>>> Foo = collections.namedtuple('Foo','a b c')
>>> weakref.ref(Foo(1,2,3))
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: cannot create weak reference to 'Foo' object
有解决办法吗?简短回答
不幸的是,非空的\uuuu插槽\uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu
变通
您所能做的最好的事情就是拥有一个不从元组继承的类
我为你写了一封信(见下文)。它是这样使用的:
from __future__ import print_function
from altnamedtuple import AltNamedTuple
from weakref import proxy
class Point(AltNamedTuple):
__slots__ = ('x', 'y', '__weakref__')
def __init__(self, x, y):
self.x = x
self.y = y
# Now, exercise the capabilities of the named tuple alternative
p = Point(10, 20)
r = proxy(p)
print(len(r)) # sizeable
print(r[0]) # indexed access
print(r.y) # attribute access
print(list(r)) # iterable
x, y = r # unpackable
print(x, y)
print(20 in r) # membership testing
print(tuple(reversed(p))) # reversible
print(r == (10, 20)) # equality
print(r != (30, 40)) # inequality
print(hash(p)) # hashable
print(r) # nice repr
print(r._asdict()) # conversion to a dict
print(r._replace(y=2))
t = (11, 22)
print(r.count(10))
print(r.index(20))
print(Point._make(t)) # alternative constructor
注意,weakrefs代理不会传递对uuu散列或uuu反向的调用。这是任何类都无法克服的固有限制
AltNamedTuple的源代码
以下是完成所有工作的课程:
class AltNamedTuple(object):
"Subclasser needs to define: __slots__ and __init__"
__slots__ = ()
def __getattr__(self, attr):
if attr != '_fields': raise AttributeError(attr)
if '__weakref__' in self.__slots__:
return self.__slots__[:-1]
return self.__slots__
def __len__(self):
return len(self._fields)
def __getitem__(self, index):
attr = self._fields[index]
return getattr(self, attr)
def __iter__(self):
for attr in self._fields:
yield getattr(self, attr)
def __reversed__(self):
return iter(reversed(tuple(self)))
def __eq__(self, other):
return tuple(self) == tuple(other)
def __ne__(self, other):
return tuple(self) != tuple(other)
def __hash__(self):
return hash(tuple(self))
def __repr__(self):
pairs = ['%s=%r' % (a, getattr(self, a)) for a in self._fields]
return ('%s(%s)' % (self.__class__.__name__, ', '.join(pairs)))
@classmethod
def _make(cls, iterable):
return cls(*iterable)
def _asdict(self):
return dict(zip(self._fields, self))
def _replace(_self, **kwds):
d = _self._asdict()
d.update(kwds)
return _self.__class__(**d)
def count(self, value):
return tuple(self).count(value)
def index(self, value):
return tuple(self).index(value)
class AltNamedTuple(object):
"Subclasser needs to define: __slots__ and __init__"
__slots__ = ()
def __getattr__(self, attr):
if attr != '_fields': raise AttributeError(attr)
if '__weakref__' in self.__slots__:
return self.__slots__[:-1]
return self.__slots__
def __len__(self):
return len(self._fields)
def __getitem__(self, index):
attr = self._fields[index]
return getattr(self, attr)
def __iter__(self):
for attr in self._fields:
yield getattr(self, attr)
def __reversed__(self):
return iter(reversed(tuple(self)))
def __eq__(self, other):
return tuple(self) == tuple(other)
def __ne__(self, other):
return tuple(self) != tuple(other)
def __hash__(self):
return hash(tuple(self))
def __repr__(self):
pairs = ['%s=%r' % (a, getattr(self, a)) for a in self._fields]
return ('%s(%s)' % (self.__class__.__name__, ', '.join(pairs)))
@classmethod
def _make(cls, iterable):
return cls(*iterable)
def _asdict(self):
return dict(zip(self._fields, self))
def _replace(_self, **kwds):
d = _self._asdict()
d.update(kwds)
return _self.__class__(**d)
def count(self, value):
return tuple(self).count(value)
def index(self, value):
return tuple(self).index(value)