[Tutor] s[len(s):len(s)] = [x] ??

[Lie Ryan]

> You can do it with slice assignment too:
> >>> a = [1, 2, 3, 4]
> >>> a[1:3] = [[7, 8]]
> >>> a
> [1, [7, 8], 4]
> 
> Now, which way is better?  The answer depends on context.  The best
> way to write it is in the manner that it makes the most sense to
> someone reading your program (including you, several years later)!

I think that the current behavior in python makes sense according to
python's slicing model: which is cursor-like behavior. List slice (and
indexing) in python is done on the model of a cursor:

0   1   2   3   
+---+---+---+---+
| A | B | C | D |
+---+---+---+---+
-4  -3  -2  -1  0

Cursor-like behavior of list in python is similar to the "typing
cursor", if you, for example, highlights letter B and C (i.e. taking
slice [1:3]) then pasted another string of letters, the result would be
the pasted string replaced the highlighted object (i.e. the slice is
gone and the inserted list become a sublist that replaced the sliced
one). If the pasted list have been inserted instead, it wouldn't fit the
cursor model.

On an aside, I'm interested in seeing how this would be parsed by python
l = [1, 2, 3, 4, 5, 6, 7, 8, 9]
l[2:8:2] = [...]

It turns out that assigning to extended slice notation require that you
to have the same length sequence on both sides, just as expected, python
doesn't do some voodoo magic for this since: "In the face of ambiguity,
refuse the temptation to guess" and "There should be one -- and
preferably only one -- obvious way to do it" [import this].
.