When a Python program assigns integers to variables, thus giving a name to a value, integer objects need to be created for them. Integers like 0, -1 or small integers are very common in programs. For integer object creation, use and destruction to be efficient for these common values, these objects are created only once and cached to be used for any variable that need such a value.
The range of integers that are cached by Python is specific to the implementation. But, this can be discovered easily by using the is operator, which returns True is two names are refer to the same object.
On my Python 3.2 64-bit CPython implementation, the range of integers that are cached seems to be
Tried with: Python 3.2 64-bit on Windows 7