[docs] [issue32288] Inconsistent behavior with slice assignment?

[Massimiliano Culpo]

Massimiliano Culpo <massimiliano.culpo at googlemail.com> added the comment:

Steven and Stefan, thanks for the quick replies, even though they are giving slightly different answers to the same questions :-)

@steven.daprano
> You refer to the docs that specify extended syntax as [start:stop:step] but then you tried [start:stop,step] which is correctly an error. (Notice the comma instead of colon.)

Maybe you missed the quote from the docs: "For example: a[start:stop:step] or a[start:stop, i]"

You say that the docs "specify extended syntax as [start:stop:step]". Apparently you're also surprised this syntax exists, and didn't notice that the error is not a SyntaxError, but a TypeError. I argue then that the syntax is there. If I get correctly what @skrah says, he seems to suggest that the syntax is there, but no built-in type is using it. Am I right?

> And again, your third issue to do with list.insert ... what is your actual bug report? Have you found an example where these aren't equivalent?

I didn't say that. I actually said "`insert` really behaves like `s[i:i] = [x]`". But the docs from the interpreter say:
```
help(list.insert)
Help on method_descriptor:
insert(...)
    L.insert(index, object) -- insert object before index

```
What does it mean to insert an object before index 101 or -101 of a 4 items list? I think if the help said "-- same as L[index:index] = [object]" I would have been fine with it.

> Please don't report three issues under one ticket, unless they are so closely related that they cannot be separated.

Apologies if this was not correct (I see you started an issue with a smaller scope). But I thought they were closely related, because all three might have been fixed by a rewording of a few parts of the docs dealing with slices.

@skrah
> I see the first issue now and I agree that Python behaves strangely.

To be clear, I don't have issues with:
```
>>> lst = [1,2,3]
>>> lst[1:2] = [1,2,3,4,5]
>>> lst
[1, 1, 2, 3, 4, 5, 3]
```
in Python, which probably is a widely used idiom to modify lists. 

My concerns are with the fact that you get the same behavior when you use `lst[1:2:1]` (which in my understanding is an extended slice), but you get a `ValueError` for any other value of `slice.step`. That might be something worth clarifying as part of issue32289 maybe?

----------

_______________________________________
Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue32288>
_______________________________________