On: The PEPs of Python 3.9

[kgm]

Though "when" the object is created isn't always so straightforward:

  >>> x = 257
  >>> y = 257
  >>> x is y
  False
  >>> def f():
  ...     x = 257
  ...     y = 257
  ...     return x is y
  ...
  >>> f()
  True

The lesson being that `is` is essentially meaningless for immutable objects, and to always use `==`.

[pansa2 → kgm]

> `is` is essentially meaningless for immutable objects

OTOH it’s recommended to use `is` rather than `==` when comparing to “singletons like `None`”.

https://www.python.org/dev/peps/pep-0008/#programming-recomm...

[joppy → pansa2]

What is the rationale behind this? '==' works all the time, and 'is' only works sometimes. Using 'is' wherever possible requires the user to know some rather arbitrary language details (which objects are singletons and which are not), wheras '==' will always give the correct answer regardless.

[pansa2 → joppy]

Classes can overload `==`:

    class C:
        def __eq__(self, other):
            return True

    print(C() == None)  # True
    print(C() is None)  # False