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Groups > comp.lang.python > #99818
| From | Terry Reedy <tjreedy@udel.edu> |
|---|---|
| Newsgroups | comp.lang.python |
| Subject | Re: Could you explain this rebinding (or some other action) on "nums = nums"? |
| Date | 2015-12-01 16:18 -0500 |
| Message-ID | <mailman.84.1449004772.14615.python-list@python.org> (permalink) |
| References | <94c2e42e-1e5f-40cf-9259-26035e277bf3@googlegroups.com> <mailman.37.1435191416.3674.python-list@python.org> <b48d4b38-a28a-4408-8271-f79e850f453f@googlegroups.com> <mailman.51.1448940760.14615.python-list@python.org> <n3l050$l7a$4@dont-email.me> |
On 12/1/2015 3:32 PM, Denis McMahon wrote: > On Tue, 01 Dec 2015 03:32:31 +0000, MRAB wrote: > >> In the case of: >> >> tup[1] += [6, 7] >> >> what it's trying to do is: >> >> tup[1] = tup[1].__iadd__([6, 7]) >> >> tup[1] refers to a list, and the __iadd__ method _does_ mutate it, but >> then Python tries to put the result that the method returns into tup[1]. >> That fails because tup itself is a tuple, which is immutable. > > I think I might have found a bug: What you found is an specific example of what MRAB said in general above. > $ python > Python 2.7.3 (default, Jun 22 2015, 19:33:41) > [GCC 4.6.3] on linux2 > Type "help", "copyright", "credits" or "license" for more information. >>>> tup = [1,2,3],[4,5,6] >>>> tup > ([1, 2, 3], [4, 5, 6]) >>>> tup[1] > [4, 5, 6] >>>> tup[1] += [7,8,9] > Traceback (most recent call last): > File "<stdin>", line 1, in <module> > TypeError: 'tuple' object does not support item assignment The bug is trying to replace a member of a tuple. The correct code, to avoid the exception while extending the list, is tup[1].extend([7,8,9]) >>>> tup[1] > [4, 5, 6, 7, 8, 9] -- Terry Jan Reedy
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Re: Could you explain this rebinding (or some other action) on "nums = nums"? fl <rxjwg98@gmail.com> - 2015-11-30 18:14 -0800
Re: Could you explain this rebinding (or some other action) on "nums = nums"? MRAB <python@mrabarnett.plus.com> - 2015-12-01 03:32 +0000
Re: Could you explain this rebinding (or some other action) on "nums = nums"? Denis McMahon <denismfmcmahon@gmail.com> - 2015-12-01 20:32 +0000
Re: Could you explain this rebinding (or some other action) on "nums = nums"? Ian Kelly <ian.g.kelly@gmail.com> - 2015-12-01 14:44 -0600
Re: Could you explain this rebinding (or some other action) on "nums = nums"? Denis McMahon <denismfmcmahon@gmail.com> - 2015-12-01 21:37 +0000
Re: Could you explain this rebinding (or some other action) on "nums = nums"? Erik <python@lucidity.plus.com> - 2015-12-01 22:34 +0000
Re: Could you explain this rebinding (or some other action) on "nums = nums"? Erik <python@lucidity.plus.com> - 2015-12-01 22:44 +0000
Re: Could you explain this rebinding (or some other action) on "nums = nums"? Terry Reedy <tjreedy@udel.edu> - 2015-12-01 16:18 -0500
Re: Could you explain this rebinding (or some other action) on "nums = nums"? Denis McMahon <denismfmcmahon@gmail.com> - 2015-12-01 21:36 +0000
Re: Could you explain this rebinding (or some other action) on "nums = nums"? Terry Reedy <tjreedy@udel.edu> - 2015-12-01 17:37 -0500
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