Why the list creates in two different ways? Does it cause by the mutability of its elements? Where the Python document explains it?

[Chris Angelico]

On Wed, Jun 16, 2021 at 2:18 AM Dieter Maurer <dieter at handshake.de> wrote:
>
> Chris Angelico wrote at 2021-6-15 19:08 +1000:
> >On Tue, Jun 15, 2021 at 6:32 PM Dieter Maurer <dieter at handshake.de> wrote:
> >>
> >> Chris Angelico wrote at 2021-6-15 05:35 +1000:
> >> >On Tue, Jun 15, 2021 at 5:12 AM Jach Feng <jfong at ms4.hinet.net> wrote:
> >> >>
> >> >> >>> n = [(1,2) for i in range(3)]
> >> >> >>> n
> >> >> [(1, 2), (1, 2), (1, 2)]
> >> >> >>> id(n[0]) == id(n[1])  == id(n[2])
> >> >> True
> >> >
> >> >This is three tuples. Tuples are immutable and you get three
> >> >references to the same thing.
> >>
> >> In addition: object identity (as revealed by `id(...)`) is
> >> an implementation detail. Do not rely on it!
> >
> >Hmm, not always. In this case, object identity isn't guaranteed -
> >every literal could give you a unique object - but in other cases,
> >object identity is a language guarantee. For instance:
>
> As far as I know, there are no guarantees are the language level.
> There are some (partially documented) implementation details
> for CPython (which is just one possible implementation).

Yes there are - plenty of them :) The example I gave is a language
guarantee. Object identity is maintained in various places, and MUST
be; in fact, I've heard tell that PyPy actually has to do some
shenanigans to ensure that identities can be tracked across certain
types of optimizations (where the object mightn't actually exist
temporarily).

ChrisA