Re: how to get the ordinal number in list

Newsgroups	comp.lang.python
Date	2014-08-10 10:34 -0700
References	(3 earlier) <53e59035$0$29998$c3e8da3$5496439d@news.astraweb.com> <338e8fb0-c9ec-462a-b560-1c1ff77de17e@googlegroups.com> <roy-3060CA.11342209082014@news.panix.com> <b5ac5b12-cda7-464e-9c14-63ef184a7a10@googlegroups.com> <roy-FEFEEE.13102110082014@news.panix.com>
Message-ID	<154cc342-7f85-4d16-b636-a1a953913c98@googlegroups.com> (permalink)
Subject	Re: how to get the ordinal number in list
From	Rustom Mody <rustompmody@gmail.com>

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On Sunday, August 10, 2014 10:40:21 PM UTC+5:30, Roy Smith wrote:
>  Rustom Mody  wrote:

> > > They haven't figured out yet that the 
> > > first step to solving a problem is to decide what algorithms you're 
> > > going to use, and only then can you start translating that into code.  
> > > They need to be led in small steps towards basic knowledge.
> > [...]
> > In my view this is starting from the wrong end.
> > I do not need to know which kind of adder the hardware is implementing to
> > use +, which sorting algorithm to use sort, etc.

> Well, no, but if the problem is, "Find the 5 largest numbers in a list", 
> you might start solving the problem by thinking, "OK, first I'm going to 
> sort the list into descending order, then I'm going to take the first 
> five items from that"(*)  Only then would you get down to "OK, how do I 
> sort a list of numbers in this language", and "OK, how do I select the 
> first five items from a list in this language".  That's what I mean by 
> first you come up with an algorithm, then you implement it in code.

>>> l= [6,2,9,12,1,4]
>>> sorted(l,reverse=True)[:5]
[12, 9, 6, 4, 2]

No need to know how sorted works nor [:5]

Now you (or Steven) can call it abstract.

And yet its 
1. Actual running code in the interpreter
2. Its as close as one can get to a literal translation of your
   "Find the 5 largest numbers in a list"

Yeah the reverse=True is a fly in the ointment.

I can do

>>> sorted(l)[-5:]
[2, 4, 6, 9, 12]

But that's a bit arcane

In any case coming back to the point

All the above are clearer than loops+assignments and can be 
taught before them

Thread

Re: how to get the ordinal number in list luofeiyu <elearn2014@gmail.com> - 2014-08-09 10:35 -0700
  Re: how to get the ordinal number in list Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-08-09 13:06 +1000
    Re: how to get the ordinal number in list Rustom Mody <rustompmody@gmail.com> - 2014-08-08 20:48 -0700
      Re: how to get the ordinal number in list Roy Smith <roy@panix.com> - 2014-08-09 11:34 -0400
        Re: how to get the ordinal number in list Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-08-10 09:43 +1000
        Re: how to get the ordinal number in list Rustom Mody <rustompmody@gmail.com> - 2014-08-10 09:28 -0700
          Re: how to get the ordinal number in list Roy Smith <roy@panix.com> - 2014-08-10 13:10 -0400
            Re: how to get the ordinal number in list Rustom Mody <rustompmody@gmail.com> - 2014-08-10 10:34 -0700
              Re: how to get the ordinal number in list Roy Smith <roy@panix.com> - 2014-08-10 14:14 -0400
                Re: how to get the ordinal number in list Rustom Mody <rustompmody@gmail.com> - 2014-08-10 11:26 -0700
                Re: how to get the ordinal number in list Chris Angelico <rosuav@gmail.com> - 2014-08-11 05:03 +1000
                Re: how to get the ordinal number in list Marko Rauhamaa <marko@pacujo.net> - 2014-08-10 22:14 +0300
                Re: how to get the ordinal number in list Chris Angelico <rosuav@gmail.com> - 2014-08-11 05:20 +1000
                Re: how to get the ordinal number in list Rustom Mody <rustompmody@gmail.com> - 2014-08-10 22:23 -0700
                Re: how to get the ordinal number in list Chris Angelico <rosuav@gmail.com> - 2014-08-11 15:46 +1000
                Re: how to get the ordinal number in list Rustom Mody <rustompmody@gmail.com> - 2014-08-10 23:22 -0700
                Re: how to get the ordinal number in list Steven D'Aprano <steve@pearwood.info> - 2014-08-11 08:55 +0000
                Re: how to get the ordinal number in list Chris Angelico <rosuav@gmail.com> - 2014-08-11 19:15 +1000
                Re: how to get the ordinal number in list Marko Rauhamaa <marko@pacujo.net> - 2014-08-11 12:35 +0300
                Re: how to get the ordinal number in list Chris Angelico <rosuav@gmail.com> - 2014-08-11 19:51 +1000
                Re: how to get the ordinal number in list Marko Rauhamaa <marko@pacujo.net> - 2014-08-11 13:46 +0300
                Re: how to get the ordinal number in list Chris Angelico <rosuav@gmail.com> - 2014-08-11 21:06 +1000
                Re: how to get the ordinal number in list Steven D'Aprano <steve@pearwood.info> - 2014-08-11 09:44 +0000
                Re: how to get the ordinal number in list Chris Angelico <rosuav@gmail.com> - 2014-08-11 19:53 +1000
                Re: how to get the ordinal number in list Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-08-11 21:30 +1000
                Re: how to get the ordinal number in list Chris Angelico <rosuav@gmail.com> - 2014-08-11 20:07 +1000
                Re: how to get the ordinal number in list Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-08-13 10:47 +1000
                Re: how to get the ordinal number in list Chris Angelico <rosuav@gmail.com> - 2014-08-13 11:31 +1000
                Re: how to get the ordinal number in list Roy Smith <roy@panix.com> - 2014-08-12 21:45 -0400
                Re: how to get the ordinal number in list Chris Angelico <rosuav@gmail.com> - 2014-08-13 12:06 +1000
                Re: how to get the ordinal number in list Roy Smith <roy@panix.com> - 2014-08-11 07:55 -0400
                Re: how to get the ordinal number in list Tim Chase <python.list@tim.thechases.com> - 2014-08-11 07:30 -0500
                Re: how to get the ordinal number in list Marko Rauhamaa <marko@pacujo.net> - 2014-08-11 15:41 +0300
                Re: how to get the ordinal number in list Chris Angelico <rosuav@gmail.com> - 2014-08-11 22:53 +1000
                Re: how to get the ordinal number in list Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-08-11 14:57 +0100
                Re: how to get the ordinal number in list Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-08-10 21:32 +0100
                Re: how to get the ordinal number in list Roy Smith <roy@panix.com> - 2014-08-10 18:01 -0400
                Re: how to get the ordinal number in list Chris Angelico <rosuav@gmail.com> - 2014-08-11 08:43 +1000
                Re: how to get the ordinal number in list Rustom Mody <rustompmody@gmail.com> - 2014-08-10 20:35 -0700
                Re: how to get the ordinal number in list Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-08-11 12:04 +1000
                Re: how to get the ordinal number in list Robert Kern <robert.kern@gmail.com> - 2014-08-11 12:56 +0100
                Re: how to get the ordinal number in list Rustom Mody <rustompmody@gmail.com> - 2014-08-11 05:11 -0700
                Re: how to get the ordinal number in list Chris Angelico <rosuav@gmail.com> - 2014-08-11 22:45 +1000
                Re: how to get the ordinal number in list Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-08-11 15:01 +0100
                Re: how to get the ordinal number in list alister <alister.nospam.ware@ntlworld.com> - 2014-08-11 12:30 +0000
                Re: how to get the ordinal number in list Marko Rauhamaa <marko@pacujo.net> - 2014-08-11 15:41 +0300
                Re: how to get the ordinal number in list Robin Becker <robin@reportlab.com> - 2014-08-11 15:32 +0100
                Re: how to get the ordinal number in list Terry Reedy <tjreedy@udel.edu> - 2014-08-11 18:01 -0400
                Re: how to get the ordinal number in list Chris Angelico <rosuav@gmail.com> - 2014-08-12 09:27 +1000
                Re: how to get the ordinal number in list wxjmfauth@gmail.com - 2014-08-12 00:21 -0700
                Re: how to get the ordinal number in list alister <alister.nospam.ware@ntlworld.com> - 2014-08-12 10:40 +0000
                Re: how to get the ordinal number in list Chris Angelico <rosuav@gmail.com> - 2014-08-12 23:39 +1000
                Re: how to get the ordinal number in list alister <alister.nospam.ware@ntlworld.com> - 2014-08-12 18:45 +0000
                Re: how to get the ordinal number in list Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-08-12 20:16 +0100
                Re: how to get the ordinal number in list "Neil D. Cerutti" <neilc@norwich.edu> - 2014-08-12 13:40 -0400
                Re: how to get the ordinal number in list Rustom Mody <rustompmody@gmail.com> - 2014-08-12 11:20 -0700
                Re: how to get the ordinal number in list "Neil D. Cerutti" <neilc@norwich.edu> - 2014-08-12 15:29 -0400
                Re: how to get the ordinal number in list Rustom Mody <rustompmody@gmail.com> - 2014-08-12 20:49 -0700
                Re: how to get the ordinal number in list Terry Reedy <tjreedy@udel.edu> - 2014-08-12 18:01 -0400
              Re: how to get the ordinal number in list Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-08-11 13:00 +1000
                Re: how to get the ordinal number in list Rustom Mody <rustompmody@gmail.com> - 2014-08-10 21:29 -0700
                Re: how to get the ordinal number in list Steven D'Aprano <steve@pearwood.info> - 2014-08-11 10:28 +0000
                Re: how to get the ordinal number in list Rustom Mody <rustompmody@gmail.com> - 2014-08-11 04:49 -0700
                Re: how to get the ordinal number in list Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-08-13 12:11 +1000
                Re: how to get the ordinal number in list Chris Angelico <rosuav@gmail.com> - 2014-08-13 12:18 +1000
                Re: how to get the ordinal number in list Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-08-13 13:11 +1000
          Re: how to get the ordinal number in list Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-08-11 03:17 +1000

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