Re: [Python-Dev] List insert at index that is well out of range - behaves like append

This functionality has existed since the earliest days of Python, and even
if we all agreed it was wrong we couldn't change it -- it would just break
too much existing code. I can't quite remember why I did it that way but it
was definitely a conscious choice; probably some symmetry or edge case.
(Note that it works this way at the other end too -- a.insert(-100, x) will
insert x at the beginning of a, if a has fewer than 100 elements.)

On Mon, Sep 15, 2014 at 3:29 PM, Mark Shannon <m...@hotpy.org> wrote:

>>> On 15/09/14 12:31, Tal Einat wrote:>>> On Mon, Sep 15, 2014 at 6:18 AM, Harish Tech <tech...@gmail.com>>> wrote:>>>>> I had a list>>>>>>   a = [1, 2, 3]>>>>>> when I did>>>>>> a.insert(100, 100)>>>>>> [1, 2, 3, 100]>>>>>> as list was originally of size 4 and I was trying to insert value at>>> index>>> 100 , it behaved like append instead of throwing any errors as I was>>> trying>>> to insert in an index that did not even existed .>>>>>>>>> Should it not throw>>>>>>>>> IndexError: list assignment index out of range>>>>>>>>> exception as it throws when I attempt doing>>>>>>>>> a[100] = 100>>>>>> Question : 1. Any idea Why has it been designed to silently handle this>>> instead of informing the user with an exception ?>>>>>>>>> Personal Opinion : Lets see how other dynamic languages behave in such a>>> situation : Ruby :>>>>>>>>>      > a = [1, 2]>>>>>>      > a[100] = 100>>>>>>      > a>>>>>>   => [1, 2, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil,>>> nil,>>> nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil,>>> nil,>>> nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil,>>> nil,>>> nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil,>>> nil,>>> nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil,>>> nil,>>> nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil,>>> nil,>>> nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, 100]>>>>>> The way ruby handles this is pretty clear and sounds meaningful (and>>> this is>>> how I expected to behave and it behaved as per my expectation) at least>>> to>>> me . So what I felt was either it should throw exception or do the way>>> ruby>>> handles it .>>>>>>>>> Is ruby way of handling not the obvious way ?>>>>>> I even raised it in stackoverflow>>> http://stackoverflow.com/questions/25840177/list->>> insert-at-index-that-is-well-out-of-range-behaves-like-append>>>>>> and got some responses .>>>>>>> Hello Harish,>>>> The appropriate place to ask questions like this is python-list [1],>> or perhaps Stack Overflow.>>>> I think this is an OK forum for this question.> If someone isn't sure if something is a bug or not, then why not ask here> before reporting it on the bug tracker?>> This does seem strange behaviour, and the documentation for list.insert> gives no clue as to why this behaviour was chosen.>> Cheers,> Mark.>> _______________________________________________> Python-Dev mailing list> Pyth...@python.org> https://mail.python.org/mailman/listinfo/python-dev> Unsubscribe: https://mail.python.org/mailman/options/python-dev/> guido%40python.org>



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--Guido van Rossum (python.org/~guido)