Small integer caching

Question

Accepted Answer

CPython caches (interns) small integers from -5 to 256. For these values, a = 256 and b = 256 both bind to the same cached object, so 'a is b' is True. With a = 257; b = 257, you'd get False in a script (though the interactive REPL may still return True due to compile-time optimisation). This is an implementation detail - never rely on 'is' for integer comparison in production code.