[Tutor] 'slice', etc

[spir]

Hello,

How does slicing in Python really work? Apparently, there are slice objects 
(start, past-end, step), generated using either the 'slice' builtin func or the 
extended slicing syntax [i:k:s]. Is this correct? [1]

Does (only) the extended syntax (always) trigger slicing instead of contructing 
a new subsequence? (new substring or sublist or whatever, actually holding a 
section of the original sequence)

Are slices and subsequences transparently usable one for the other?

Does python internally choose whether it is best to do make a slice or 
subsequence? If yes, does it also at times conversely  make a slice instead of a 
subsequence, when using the shorter syntax [i:k] (or even [i] for s string)? [2]

PS: I searched but could not find a PEP specifically dedicated to 'slice' only. 
Pointers welcome, especially to docs explaining purpose, rationale, design, 
etc... Maybe this means slices have always existed and I just missed them totally?

Thank you,
Denis

[1] I discovered that by chance; apparently, this is recent or I missed the 
feature when I used to code in python commonly, years, ago. I only noted it now 
because my favorite editor highlighted 'slice' as a Py builtin id!

[2] The fact that slices exist at all shows how worth it is to avoid needlessly 
creating subsequences, at least in whole categories of case; but this is 
certainly not always true, especially for very short strings, maybe other short 
subseqs of short items.

[3] PEP 357 "Allowing Any Object to be Used for Slicing" is an extension about 
__index__.
http://www.python.org/dev/peps/pep-0357/