Alain Ketterlin <al...@universite-de-strasbourg.fr.invalid>:
> Grant Edwards <invalid@invalid.invalid> writes:
>
> [...]
>> Or to be a bit obtuse: Python parameters are passed by value, but all
>> values are references.
>
> Exactly, that's a perfect description. There's is no need for a new
> name. As a corollary, all names (including "variables" and object
> attributes) are references.
We are all confusing each other because of the word "reference" means so
many things.
In Grant's explanation, a "reference" is a pointer, the invisible gluons
that bind, say, a variable to an object.
In Alain's sentence a "reference" is a variable or any other "lvalue"
that can be bound to an object.
Thus, the statement
a[3] = 4
contains the reference[Alain] "a[3]". After the statement is executed,
the reference[Alain] contains a reference[Grant] to an int object 4.
Now, is it useful to make the distinction and use the verb "contain?"
Yes, it is. Consider these statements:
a[0] = 4
a[1] = 4
a[2] = a[1]
Now, "a[0]", "a[1]" and "a[2]" are three separate references[Alain].
However between the three, they contain a maximum of two distinct
references[Grant], which can be ascertained with an "is" test:
a[2] is a[1]
=> True
So while the references[Grant] are identical, the references[Alain] are
not. If I'm not mistaken, Python has no means of comparing the
identities of references[Alain].
Marko
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