how to get the ordinal number in list

[Neil D. Cerutti]

On 8/10/2014 2:14 PM, Roy Smith wrote:
> In article <154cc342-7f85-4d16-b636-a1a953913c98 at googlegroups.com>,
>   Rustom Mody <rustompmody at gmail.com> wrote:
>
>>>>> 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"
>> [...]
>> All the above are clearer than loops+assignments and can be
>> taught before them
>
> I disagree.  For a beginner, you want to be able to break things down
> into individual steps and examine the result at each point.  If you do:
>
>>>>> l= [6,2,9,12,1,4]
>>>>> l2 = sorted(l,reverse=True)
>
> you have the advantage that you can stop after creating l2 and print it
> out.  The student can see that it has indeed been sorted.  With the
> chained operations, you have to build a mental image of an anonymous,
> temporary list, and then perform the slicing operation on that.  Sure,
> it's the way you or I would write it in production code, but for a
> beginner, breaking it down into smaller pieces makes it easier to
> understand.
>
>>>>> l2[:5]

Yes, and that teaching technique is supported by research.

Beginners are particularly poor, in relation to experts, at noticing the 
applicability of idea, and at combining ideas together. Breaking things 
into component parts has multiple benefits:

1. The applicability of individual ideas becomes obvious. It's one thing 
to know about [].sort, and another thing to know when it's appropriate 
to sort something.

2. The expert specifically shows how and why the ideas are combined. 
This helps build the connection for the beginner, whose knowledge is not 
stored as an expert stores it; i.e, in broad categories with multiple 
connections; but as disorganized data with very few connections.

http://www.amazon.com/How-Learning-Works-Research-Based-Principles/dp/0470484101

I bought the book based on a recommendation from SciPy talk, and it's 
really great. As an autodidact, it'll help me teach *myself* better, too.

-- 
Neil Cerutti