由于历史原因（阅读：可怕的type(t) == tuple检查），我发现自己需要冻结圆形图作为tuple对象的集合。显然，这并不理想：
>>> head = ("head",None)
>>> a = ("a",("b",("c",head)))
>>> head[1] = a
Traceback (most recent call last):
File "<pyshell#3>",line 1,in <module>
head[1] = a
TypeError: 'tuple' object does not support item assignment
但是，我并不是TypeError的真正信奉者，并且怀疑通过特定于实现的黑客手段可以做到这一点。
但是，我并不是TypeErrors的真正拥护者，并且怀疑通过特定于实现的黑客，可以做到这一点。
可悲的是，您是正确的：
from ctypes import Structure,c_ssize_t,c_void_p,py_object,pythonapi
pythonapi.Py_DecRef.argtypes = py_object,def mutable(tup):
# We are generating this class dynamically because the size of ob_item
# varies according to the size of the given tuple
class PyTupleObject(Structure):
_fields_ = [('ob_refcnt',c_ssize_t),('ob_type',c_void_p),('ob_size',('ob_item',py_object * len(tup))]
@classmethod
def from_tuple(cls,tup):
instance = cls.from_address(id(tup))
# Save a reference to tup on the instance,as we are using it directly from memory
# and don't want it to be garbage collected
instance.original = tup
return instance
def __setitem__(self,idx,val):
# Replacing a value in self.ob_item doesn't decref the old value but does indref the new value
pythonapi.Py_DecRef(self.ob_item[idx])
self.ob_item[idx] = val
def __getitem__(self,idx):
return self.ob_item[idx]
def __iter__(self):
return iter(self.ob_item)
def __len__(self):
return len(self.ob_item)
def __contains__(self,val):
return val in self.ob_item
return PyTupleObject.from_tuple(tup)
if __name__ == '__main__':
tup = (None,)
mut_tup = mutable(tup)
mut_tup[0] = tup
print(tup is tup[0]) # Outputs "True"
如何产生这种怪异而又不会冒出界外或引起其他C不确定行为的危险？
我们通过将成员ob_item定义为py_object * len(tup)来防止越界访问。
垃圾回收器的循环依赖释放部分可以应付这种情况吗？
不！元组应该是不可变的，因此不希望对其具有循环引用。这就是为什么他们不实现tp_clear方法的原因，Python垃圾回收器使用该方法来中断参考周期并收集涉及的垃圾。更多详细信息here