python - 将不可变的 Python 对象传递给其构造函数后的标识

Question

我理解以下行为是 not guaranteed :

>>> x = "Hello, world!"
>>> y = "Hello, world!"
>>> assert x is y

但是，这种行为是否得到保证:

>>> x = "Hello, world!"
>>> y = str(x)
>>> assert x is y

如果是这样，在我自己的(不可变)类中实现此行为的正确方法是什么？

---

编辑:“此行为”是指“应重用现有实例的类的构造函数”:

>>> x = MyClass("abc", 123)
>>> y = MyClass(x)
>>> assert x is y

Answer 1

覆盖 __new__() 以返回传入的对象:

class C(object):
  def __new__(cls, ref):
    if isinstance(ref, C):
      return ref
    else:
      return super(C, cls).__new__(cls)

  def __init__(self, ref):
    if self is not ref:
      self.x = ref

c1=C(7)
c2=C(13)
assert c1 is not c2
c3=C(c1)
assert c1 is c3