Re: Python 3: dict & dict.keys()

From	Peter Otten <__peter__@web.de>
Subject	Re: Python 3: dict & dict.keys()
Date	2013-07-25 18:25 +0200
Organization	None
References	(3 earlier) <mailman.5061.1374692206.3114.python-list@python.org> <51f0ce06$0$29971$c3e8da3$5496439d@news.astraweb.com> <CAPTjJmoFw-tM0itPJFBqO37fPBM9UHTosCACy2Xy0Wjm2dgZmQ@mail.gmail.com> <ksqmmk$lq2$1@ger.gmane.org> <CALwzid=NQNijkX_JXyoGnMRjV+t6i4uFGGfjKGKid=BvUkx42w@mail.gmail.com>
Newsgroups	comp.lang.python
Message-ID	<mailman.5111.1374769510.3114.python-list@python.org> (permalink)

Show all headers | View raw

Ian Kelly wrote:

> On Thu, Jul 25, 2013 at 2:13 AM, Peter Otten <__peter__@web.de> wrote:
>> Chris Angelico wrote:
>>
>>> On Thu, Jul 25, 2013 at 5:04 PM, Steven D'Aprano
>>> <steve+comp.lang.python@pearwood.info> wrote:
>>>> - Views support efficient (O(1) in the case of keys) membership
>>>> testing, which neither iterkeys() nor Python2 keys() does.
>>>
>>> To save me the trouble and potential error of digging through the
>>> source code: What's the complexity of membership testing on
>>> values/items? Since you're calling it "efficient" it must be better
>>> than O(n) which the list form would be, yet it isn't O(1) or you
>>> wouldn't have qualified "in the case of keys". Does this mean
>>> membership testing of the values and items views is O(log n) in some
>>> way, eg a binary search?
>>
>> keys() and items() is O(1); both look up the key in the dictionary and
>> items() then proceeds to compare the value. values() is O(n).
> 
> 3.x values() is O(n) but avoids the unnecessary step of copying all the
> values in the dict that you get when performing the same operation
> using 2.x values().  Hence, although the asymptotic complexity is the
> same, it's still more efficient.

In Python 2 the prudent pythonista used itervalues() to avoid unnecessary 
intermediate list...

Back to comp.lang.python | Previous | Next — Previous in thread | Find similar | Unroll thread

Thread

Re: Python 3: dict & dict.keys() Ethan Furman <ethan@stoneleaf.us> - 2013-07-24 11:31 -0700
  Re: Python 3: dict & dict.keys() alex23 <wuwei23@gmail.com> - 2013-07-25 16:01 +1000
    Re: Python 3: dict & dict.keys() Ethan Furman <ethan@stoneleaf.us> - 2013-07-25 06:47 -0700
  Re: Python 3: dict & dict.keys() Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-07-25 07:04 +0000
    Re: Python 3: dict & dict.keys() Chris Angelico <rosuav@gmail.com> - 2013-07-25 18:02 +1000
    Re: Python 3: dict & dict.keys() Peter Otten <__peter__@web.de> - 2013-07-25 10:13 +0200
    Re: Python 3: dict & dict.keys() Ian Kelly <ian.g.kelly@gmail.com> - 2013-07-25 09:53 -0600
    Re: Python 3: dict & dict.keys() Peter Otten <__peter__@web.de> - 2013-07-25 18:25 +0200

csiph-web