It's been brought up on Stack Overflow that the "in" operator (on tuples, and by my testing on dict and list, as well as dict lookup) uses object identity as a shortcut, and returns true immediately if the object being tested *is* an element of the container. However, the contains operation does not specify whether object identity or equality is to be used. In effect, the built-in container types use a hybrid test: "a is b or a == b".
My question is, is this a *correct* implementation of the operator, or are objects "supposed to" use a basis of equality for these tests? -- https://mail.python.org/mailman/listinfo/python-list
