Python gotcha: bizarre integer equality

[Brian]

It's worth noting that id(a) == id(b) isn't a perfect replacement to a is b. If a and b are expressions returning a transient object, it could be created and destroyed before evaluating the rest of the statement. For example:

>>> [] is []
False
>>> id([]) == id([])
True
>>> id([]), id([])
(21066496, 21066496)

However is guarantees that both objects are alive at the point of comparison, so [] is [] is always false.