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

[Mark Shannon]

On 15/09/14 12:31, Tal Einat wrote:
> On Mon, Sep 15, 2014 at 6:18 AM, Harish Tech <technews.full at 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.