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| From | Mark Lawrence <breamoreboy@yahoo.co.uk> |
| Subject | Re: FW: Unexpexted behaviot of python operators on list |
| Date | Tue, 25 Nov 2014 12:20:26 +0000 |
| References | <mailman.16274.1416907513.18130.python-list@python.org> <54746a98$0$12990$c3e8da3$5496439d@news.astraweb.com> |
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On 25/11/2014 11:40, Steven D'Aprano wrote: > PANDEY2 Archana (MORPHO) wrote: > >> Hello >> >> I hereby would like to share the problem I have found regarding python >> list implementation:- >> >> As per python documentation python list is mutable data object. >> >> That problem I found with the list is that is behaves differently when we >> use '+=' and '+' '=' operators separately. For example- >> a=a+1 and a +=1 both behave in same way for all data types except python >> list > > `a += b` is only *approximately* the same as `a = a+b`. The documentation > says: > > An augmented assignment expression like x += 1 can be rewritten as x = x + 1 > to achieve a similar, but not exactly equal effect. In the augmented > version, x is only evaluated once. Also, when possible, the actual > operation is performed in-place, meaning that rather than creating a new > object and assigning that to the target, the old object is modified > instead. > > https://docs.python.org/2/reference/simple_stmts.html#augmented-assignment-statements > > >> Please find the attached module and execute it on windows python32, See >> the difference in output. > > I cannot see the attached module. Did you forget to attach it, or did your > mail server delete it? > http://bugs.python.org/file37269/Operator_bug_python.py a=[1,2,3] b=a b+=[4,5] print(a) print(b) x=[1,2,3] y=x y=y+[4,5] print(x) print(y) I know that you can explain it better than I can :) -- My fellow Pythonistas, ask not what our language can do for you, ask what you can do for our language. Mark Lawrence
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FW: Unexpexted behaviot of python operators on list "PANDEY2 Archana (MORPHO)" <archana.pandey.2@morpho.com> - 2014-11-25 10:23 +0100
Re: FW: Unexpexted behaviot of python operators on list Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-11-25 22:40 +1100
Re: FW: Unexpexted behaviot of python operators on list Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-11-25 12:20 +0000
Re: FW: Unexpexted behaviot of python operators on list Denis McMahon <denismfmcmahon@gmail.com> - 2014-11-25 13:07 +0000
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