Roundup Robot added the comment:
New changeset 138f54622841 by R David Murray in branch '3.4':
#20135: FAQ entry for list mutation. (See also 6375bf34fff6.)
https://hg.python.org/cpython/rev/138f54622841
New changeset 3d924bbfdcbc by R David Murray in branch 'default':
Merge: #20135: FAQ entry
R. David Murray added the comment:
I accidentally committed the patch early to 3.4/3.5. I've now addressed Ezio's
review comment per my suggestion on the review, and committed it to 2.7 as well.
Thanks everyone for your contributions.
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resolution: - fixed
stage: commit review -
R. David Murray added the comment:
Here is my version of Ezio's patch.
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Added file: http://bugs.python.org/file36748/mutable_faq.patch
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Ezio Melotti added the comment:
Here is a new patch that includes an additional paragraph about mutation and
non-mutation operations.
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Added file: http://bugs.python.org/file36236/issue20135-2.diff
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Francis MB added the comment:
A) On the example:
+Also note that some operations (e.g. ``y.append(10)``/``y += [10]`` or
+``y.sort()``) mutate
are you saying:
1) y.append(10) divided by y += [10] or
2) y.append(10) and y += [10]
I don't want to split hairs but reading it fast confused me a
R. David Murray added the comment:
I think the example would be clarified by speaking about mutation operations
versus non-mutation operations. After all:
x = [1]
y = x
x = x + [2]
x
[1, 2]
y
[1]
At that point including a list += operation would also be beneficial.
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Ezio Melotti added the comment:
Good point, I'll try to add that to the FAQ.
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Berker Peksag added the comment:
LGTM.
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stage: needs patch - patch review
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Changes by Ezio Melotti ezio.melo...@gmail.com:
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assignee: docs@python - ezio.melotti
nosy: +rhettinger
stage: patch review - commit review
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Roundup Robot added the comment:
New changeset 3881c12fa3ae by Ezio Melotti in branch '2.7':
#20135: move FAQ about mutable default arguments to the programming FAQs page.
http://hg.python.org/cpython/rev/3881c12fa3ae
New changeset 3b7b0f5aac1e by Ezio Melotti in branch '3.4':
#20135: move FAQ
Ezio Melotti added the comment:
I moved the FAQ about mutable default arguments to the programming FAQs page.
I was going to do a review about new FAQ, but it since I had several comments I
just tried to rewrite it and make a new patch.
Do you think this is clear enough?
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Added
Mark Lawrence added the comment:
+1 from me, I thought it was crystal clear.
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versions: +Python 3.5 -Python 3.3
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M. Volz added the comment:
Thanks David,
I've updated the patch to move the default values question into the programming
FAQ where you recommended it go, and also changed the title of the mutable list
question.
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Added file: http://bugs.python.org/file34604/sortFAQ_defaultval.patch
Éric Araujo added the comment:
I agree; if someone goes to the docs, “Programming FAQ” looks more enticing
than “Design and History”.
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R. David Murray added the comment:
M. Votz: I like your entry, but I think it should be titled Why did changing
list 'a' also change list 'b'? That's the form I've always encountered this
question in. Then the answer can start of with It didn't, 'a' and 'b' are the
same list. and then go
M. Volz added the comment:
I've written and attached a patch for the list mutation question. I took a
little bit of a different tack on this and addressed a more general question
whilst still including list mutation as an example. I know the language can get
a little fussy on these sorts of
Éric Araujo added the comment:
Resources: http://nedbatchelder.com/text/names.html
http://python.net/~mwh/hacks/objectthink.html
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R. David Murray added the comment:
I'm in favor of moving the FAQ answer Ezio identified to the Programming
section, myself, but I'd like concurrence from at least one other committer
before we do it.
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Changes by M. Volz marie...@gmail.com:
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Ezio Melotti added the comment:
http://docs.python.org/3/faq/design.html#why-are-default-values-shared-between-objects
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R. David Murray added the comment:
I *thought* there was a FAQ entry for that. Didn't think to look for it in the
design section though :(. Nor is the title likely to catch the eye of someone
wondering why their default argument modifications are being unexpectedly
persistent. Also, the
Fran Bull added the comment:
I read the FAQ last night and I couldn't see these answered there either. I
would like to try submitting a patch for this one, probably this evening. It
will likely be two FAQs in the programming section that go something like:
Why does changing one list change
R. David Murray added the comment:
Thanks for working on this.
Technically, defaults are evaluated when the 'def' statement is executed, which
is normally, but not always, at the time that the module is first imported
(counterexample: nested function definitions).
The answer should also
Fran Bull added the comment:
Perhaps a 3rd FAQ something like this?:
Why is changing a list in one instance of a class also changing it in another
instance of the same class?
This happens:
class A(object):
... def __init__(self, fruit=[]):
... self.fruit = fruit
...
an_A = A()
Changes by Fran Bull fran.b...@gmail.com:
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keywords: +patch
Added file: http://bugs.python.org/file33502/20135.patch
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Changes by Terry J. Reedy tjre...@udel.edu:
--
stage: - needs patch
title: mutate list - FAQ need list mutation answers
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