Are comprehensions (list, dict, set) supposed to run faster than regular approach?
On Mon, Feb 9, 2009 at 4:30 PM, <bangpypers-requ...@python.org> wrote: > Send BangPypers mailing list submissions to > bangpypers@python.org > > To subscribe or unsubscribe via the World Wide Web, visit > http://mail.python.org/mailman/listinfo/bangpypers > or, via email, send a message with subject or body 'help' to > bangpypers-requ...@python.org > > You can reach the person managing the list at > bangpypers-ow...@python.org > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of BangPypers digest..." > > > Today's Topics: > > 1. Comprehending the comprehensions (Anand Balachandran Pillai) > 2. Looking for python Job (M Kumar) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Mon, 9 Feb 2009 12:09:46 +0530 > From: Anand Balachandran Pillai <abpil...@gmail.com> > Subject: [BangPypers] Comprehending the comprehensions > To: Bangalore Python Users Group - India <bangpypers@python.org> > Message-ID: > <8548c5f30902082239y2b0de5a6nc871e9756b595...@mail.gmail.com> > Content-Type: text/plain; charset=UTF-8 > > Python 3.0 introduces two new ways of "comprehending". > > We had list comprehensions before. Now there are set & > dict comprehensions in the language. > > Let us say there are two lists. For generating the list of unique > products of numbers in the list, in Python 2.x, this could be > done in 2 approaches. > > 1. Using a set, > > >>> l=[1,2,3,4] > >>> m=[3,4,5,6] > >>> set([x*y for x in l for y in m]) > {3, 4, 5, 6, 8, 9, 10, 12, 15, 16, 18, 20, 24} > > 2. Using a dictionary and inserting the values as keys, > > >>> l=[1,2,3,4] > >>> m=[3,4,5,6] > >>> d = {} > >>> [d.setdefault(x*y, 0) for x in l for y in m] > >>> d.keys() > [3, 4, 5, 6, 8, 9, 10, 12, 15, 16, 18, 20, 24] > >>> > > In Python 3.0, this is straight-forward using "set comprehensions". > Set comprehensions are like list comprehensions but with braces replacing > the square brackets. And they produce sets, not lists. > > So the approach (1) in py3k is a one-liner. > > >>> {x*y for x in l for y in m} > {3, 4, 5, 6, 8, 9, 10, 12, 15, 16, 18, 20, 24} > > The approach (2) is also possible, since we now have "dict comprehensions" > too! Which means you can build a dict in place without having to define one > before and using 'setdefault' etc. > > >>> d={x*y:0 for x in l for y in m} > >>> list(d.keys()) > [3, 4, 5, 6, 8, 9, 10, 12, 15, 16, 18, 20, 24] > > Note that the (list(d.keys)) is needed in Py3k since d.keys() no longer > return a list as it used to in Py 2.x, but instead returns a generator. > > Regards, > > --Anand > > > > > -- > -Anand > > > ------------------------------ > > Message: 2 > Date: Mon, 9 Feb 2009 16:25:39 +0530 > From: M Kumar <tomanis...@gmail.com> > Subject: [BangPypers] Looking for python Job > To: bangpypers@python.org > Message-ID: > <783b47270902090255t9b10a2dx695f578ed039e...@mail.gmail.com> > Content-Type: text/plain; charset="iso-8859-1" > > Hi all > > I am looking for python openings, I have 2 years experience in python > programming. If anyone come to know about any suitable openings kindly let > me know > > -- > Regards, > > Maneesh KB > > Comat Technologies > > Bangalore > > Mob: 9740-192309 > > > > We work with the underprivileged and in rural India. If you are interested > to be a part of it, please mail or call me. I will be happy to share and > inform - http://www.comat.com > -------------- next part -------------- > An HTML attachment was scrubbed... > URL: < > http://mail.python.org/pipermail/bangpypers/attachments/20090209/37f6f2e1/attachment-0001.htm > > > > ------------------------------ > > _______________________________________________ > BangPypers mailing list > BangPypers@python.org > http://mail.python.org/mailman/listinfo/bangpypers > > > End of BangPypers Digest, Vol 18, Issue 7 > ***************************************** >
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