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| Started by | Peter Otten <__peter__@web.de> |
|---|---|
| First post | 2015-05-30 09:56 +0200 |
| Last post | 2015-05-30 10:36 +0200 |
| Articles | 3 — 2 participants |
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Minus operator versus unary minus Peter Otten <__peter__@web.de> - 2015-05-30 09:56 +0200
Re: Minus operator versus unary minus Steven D'Aprano <steve@pearwood.info> - 2015-05-30 18:19 +1000
Re: Minus operator versus unary minus Peter Otten <__peter__@web.de> - 2015-05-30 10:36 +0200
| From | Peter Otten <__peter__@web.de> |
|---|---|
| Date | 2015-05-30 09:56 +0200 |
| Subject | Minus operator versus unary minus |
| Message-ID | <mailman.215.1432972613.5151.python-list@python.org> |
The following modification of the collections.Counter implementation https://hg.python.org/cpython/rev/fe4efc0032b5 was just checked in with the line result[elem] = 0 - count Does this have an advantage over the obvious result[elem] = -count ?
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| From | Steven D'Aprano <steve@pearwood.info> |
|---|---|
| Date | 2015-05-30 18:19 +1000 |
| Message-ID | <55697284$0$12992$c3e8da3$5496439d@news.astraweb.com> |
| In reply to | #91515 |
On Sat, 30 May 2015 05:56 pm, Peter Otten wrote: > The following modification of the collections.Counter implementation > > https://hg.python.org/cpython/rev/fe4efc0032b5 > > was just checked in with the line > > result[elem] = 0 - count > > Does this have an advantage over the obvious > > result[elem] = -count > > ? py> class Thingy: ... def __neg__(self): ... return [1, 2, 3, 4] ... py> -Thingy() [1, 2, 3, 4] py> 0 - Thingy() Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: unsupported operand type(s) for -: 'int' and 'Thingy' -- Steven
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| From | Peter Otten <__peter__@web.de> |
|---|---|
| Date | 2015-05-30 10:36 +0200 |
| Message-ID | <mailman.216.1432975020.5151.python-list@python.org> |
| In reply to | #91516 |
Steven D'Aprano wrote: > On Sat, 30 May 2015 05:56 pm, Peter Otten wrote: > >> The following modification of the collections.Counter implementation >> >> https://hg.python.org/cpython/rev/fe4efc0032b5 >> >> was just checked in with the line >> >> result[elem] = 0 - count >> >> Does this have an advantage over the obvious >> >> result[elem] = -count >> >> ? > > > py> class Thingy: > ... def __neg__(self): > ... return [1, 2, 3, 4] > ... > py> -Thingy() > [1, 2, 3, 4] > py> 0 - Thingy() > Traceback (most recent call last): > File "<stdin>", line 1, in <module> > TypeError: unsupported operand type(s) for -: 'int' and 'Thingy' Hm, do you have an example of a Counter (or subclass) instance where the values are not int?
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