Hi , Sorry for that mistake . Now I have posted it in python-list mailing list . Thanks for your guidance. Harish On Mon, Sep 15, 2014 at 5:01 PM, Tal Einat 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

...

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

On Mon, Sep 15, 2014 at 6:18 AM, Harish Tech wrote: trying 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-wel...

...

and got some responses .

Hello Harish,

The appropriate place to ask questions like this is python-list [1], or perhaps Stack Overflow.

If you meant to suggest changing the behavior of Python in such cases, you should first discuss this on python-list, and then post a clearly written suggestion to python-ideas [2].

This list, python-dev, is used for discussing the development *of* the Python language.

See the "Python Mailing Lists" page [3] for more information.

Regards, - Tal Einat

..[1]: http://mail.python.org/mailman/listinfo/python-list ..[2]: http://mail.python.org/mailman/listinfo/python-ideas ..[3]: https://www.python.org/community/lists/

On 15/09/2014 23:29, Mark Shannon wrote:

On 15/09/14 12:31, Tal Einat wrote:

...

On Mon, Sep 15, 2014 at 6:18 AM, Harish Tech 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-wel...

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.

I assume it's based on the concepts of slicing. From the docs "s.insert(i, x) - inserts x into s at the index given by i (same as s[i:i] = [x])". Although shouldn't that read s[i:i+1] = [x] ? -- My fellow Pythonistas, ask not what our language can do for you, ask what you can do for our language. Mark Lawrence

On Mon, 15 Sep 2014 23:46:03 +0100 Mark Lawrence wrote:

I assume it's based on the concepts of slicing. From the docs "s.insert(i, x) - inserts x into s at the index given by i (same as s[i:i] = [x])". Although shouldn't that read s[i:i+1] = [x] ?

No, the latter would replace the contents at index i, while the former inserts it (formally, it replaces the 0-length slice with a 1-length slice). Regards Antoine.

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 wrote:

On 15/09/14 12:31, Tal Einat wrote:

...

On Mon, Sep 15, 2014 at 6:18 AM, Harish Tech 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 Python-Dev@python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/ guido%40python.org

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