[Tutor] Python __del__ method

[eryk sun]

On Wed, Jul 12, 2017 at 12:07 AM, eryk sun <eryksun at gmail.com> wrote:
> On Tue, Jul 11, 2017 at 2:47 PM, Jia Yue Kee <JiaYue.Kee at firstsolar.com> wrote:
>>
>> Case 2: If I were to run the code in "Interactive Mode", the following output will be obtained:
>>
>>>>> x = Robot("Tik-Tok")
>> Tik-Tok has been created!
>>>>> y = Robot("Jenkins")
>> Jenkins has been created!
>>>>> z = x
>>>>> z
>> <__main__.Robot object at 0x02D7E910>
>>>>> x
>> <__main__.Robot object at 0x02D7E910>
>>>>> del x
>>>>> del z
>>>>> del y
>> Robot has been destroyed
>>
>> My question being why is that "Robot has been destroyed" is only printed once in Case 2
>> (interactive mode) while it is printed out twice in Case 1 (script mode)?
>
> The REPL (interactive mode) keeps a reference to the last non-None
> result as builtins `_`, for convenient access to the last result. In
> your case, it results from evaluating `x`. Thus you have a hidden
> reference that's keeping that object alive. Enter anything except None
> or _ to clear that reference.

Well, not just any statement. It has to evaluate to another object
except None or the Robot object that _ currently references. For
example, enter 42.