On Feb 23, 2009, at 3:03 , Gabriel Genellina wrote:
En Mon, 23 Feb 2009 03:54:16 -0200, Denis Kasak
<denis.ka...@gmail.com> escribió:
On Mon, Feb 23, 2009 at 5:09 AM, Steven D'Aprano
<ste...@remove.this.cybersource.com.au> wrote:
On Sun, 22 Feb 2009 13:37:27 -0300, andrew cooke wrote:
as far as i understand things, the best model is:
1 - everything is an object
2 - everything is passed by reference
Except that is wrong. If it were true, you could do this:
def swap(x, y):
y, x = x, y
a = 1
b = 2
swap(a, b)
assert a == 2 and b == 1
but you can't, it does not work. Ergo, parameter passing in
Python does
not have the same semantics as languages that use pass-by-
reference, such
as Pascal and Basic. That means that even if you can justify the
claim
"Python is pass-by-reference" by some technical argument (and I
don't
believe you can), it is misleading to make that claim without
further
qualifications.
You could, however, argue that the swap function doesn't work as
expected (e.g. from a Pascal or a C++ POV) simply because the
underlying objects aren't mutable.
That's irrelevant - mutable and immutable objects are passed
exactly the same way.
I don't think they were saying that mutable and immutable objects
were handled differently. They are different in terms of what a
function can do to them (mutate them or no). Thus, if you can't
mutate them, then the caller can't see any changes in the objects by
actions in the function so the swap won't work: it doesn't mutate the
objects at all. In the case of a list or a dict, then one can mutate
them, and the changes are seen in the caller. In both cases, the
object itself is passed the same way.
bb
--
Brian Blais
bbl...@bryant.edu
http://web.bryant.edu/~bblais
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