Ray.Allen ysj@gmail.com added the comment:
Alexander:
When a is mutable, a += b updates it in-place, so there is no ambiguity: the
type of a cannot change. When you do a + b, there is no reason to treat a as
more deserving than b when selecting the type of the result
Does this means
Alexander Belopolsky belopol...@users.sourceforge.net added the comment:
On Wed, Jul 21, 2010 at 2:09 AM, Ray.Allen rep...@bugs.python.org wrote:
..
Does this means a += b is not the same as a = a + b?
For immutable a, the two are practically the same, for mutable, they
are necessarily
Changes by Alexander Belopolsky belopol...@users.sourceforge.net:
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status: open - closed
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New submission from Dirkjan Ochtman dirk...@ochtman.nl:
This seems wrong:
a = []
b = iter(['c', 'd'])
a += b
c = []
c + iter(['d', 'e'])
Traceback (most recent call last):
File stdin, line 1, in module
TypeError: can only concatenate list (not listiterator) to list
In other words, if
Changes by Éric Araujo mer...@netwok.org:
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Amaury Forgeot d'Arc amaur...@gmail.com added the comment:
This actually works for any iterator:
l = []
l += 'abc'
l
['a', 'b', 'c']
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Amaury Forgeot d'Arc amaur...@gmail.com added the comment:
for any *iterable*!
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Alexander Belopolsky belopol...@users.sourceforge.net added the comment:
In other words, if iadd can deal with it, why can't add?
Should ['a', 'b', 'c'] + 'def' return ['a, 'b', 'c', 'd' , 'e', 'f'] or
'abcdef'?
In the face of ambiguity, refuse the temptation to guess.
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nosy:
Dirkjan Ochtman dirk...@ochtman.nl added the comment:
Sure, but:
a = ['a', 'b', 'c']
a += 'def'
a
['a', 'b', 'c', 'd', 'e', 'f']
I think either way is fine (I'm probably on the side of refusing to guess), but
what I don't understand is why a += b is different from a + b in this respect.
Alexander Belopolsky belopol...@users.sourceforge.net added the comment:
I don't understand is why a += b is different from a + b
in this respect.
When a is mutable, a += b updates it in-place, so there is no ambiguity: the
type of a cannot change. When you do a + b, there is no reason to
Changes by Alexander Belopolsky belopol...@users.sourceforge.net:
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type: - feature request
versions: +Python 3.2 -Python 2.6
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Alexander Belopolsky belopol...@users.sourceforge.net added the comment:
Note that immutable types are consistent:
x = tuple('abc')
x += 'def'
Traceback (most recent call last):
File stdin, line 1, in module
TypeError: can only concatenate tuple (not str) to tuple
x + 'def'
Traceback
Dirkjan Ochtman dirk...@ochtman.nl added the comment:
Hmm, that's pretty subtle. I guess I understand, at least.
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Changes by Alexander Belopolsky belopol...@users.sourceforge.net:
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assignee: - belopolsky
resolution: - rejected
stage: - committed/rejected
status: open - pending
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Éric Araujo mer...@netwok.org added the comment:
Alexander, why the pending status?
Dirkjan, do you think this is a doc bug?
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Alexander Belopolsky belopol...@users.sourceforge.net added the comment:
why the pending status?
To me this is a way to say I will close this next time I look unless someone
will change my mind. pending has a nice property that it will change to
open once someone adds a comment. This is
Éric Araujo mer...@netwok.org added the comment:
Thanks for the explanation of pending, I thought the mysterious Roundup/browser
bug had changed the status in my back.
Searching for __iadd__ gave me only library/collections; library/stdtypes says
very little.
I thought it was common to
Alexander Belopolsky belopol...@users.sourceforge.net added the comment:
I thought it was common to requalify a bug report into a doc bug.
That's upto you and OP. My rule of thumb is if the title reads as either code
or doc bug, it's ok to reclassify. If not, it is better to open a separate
Dirkjan Ochtman dirk...@ochtman.nl added the comment:
Hmm, I'm still not entirely sure that += shouldn't disallow this as well, just
because of the inconsistency. I understand the reasoning now, but it feels like
maybe it should be an implementation detail, and it should just be disallowed
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