Add notes about `s[i]` in `Common Sequence Operations`

[Yzi-Li]

Documentation

Operation	Result	Notes
s[i]	ith item of s, origin 0	(3)

3. If i or j is negative, the index is relative to the end of sequence s: len(s) + i or len(s) + j is substituted. But note that -0 is still 0.

We can add a note: If the sequence is empty or i is outside the sequence range, IndexError will be raised.

Linked PRs

• gh-134976: document the exception type that can be raised by s[i] #134977
• [3.14] gh-134976: document the exception type that can be raised by s[i] (GH-134977) #135258
• [3.13] gh-134976: document the exception type that can be raised by s[i] (GH-134977) #135259

[picnixz]

I'm surprised that there is nothing about IndexError on this page

[terryjreedy]

I believe that while negative indexes are implemented for (most?) builtins, this is not necessarily the case for all sequences.

[picnixz]

Note (3) still says:

If i or j is negative, the index is relative to the end of sequence s: len(s) + i or len(s) + j is substituted. But note that -0 is still 0.

So the common sequence operations assume that negative indices should be supported by arbitrary sequences.

[picnixz]

Thank you!