[Tutor] mapping/filtering a sequence

[Mark Tolonen]

"Douglas Philips" <dgou at mac.com> wrote in message 
news:6A3250C7-31B6-4958-8E0A-F538989ED4F9 at mac.com...
> On or about 2009 Sep 5, at 10:45 AM, Martin A. Brown indited:
>> Have you discovered the map() builtin yet?
>>
>> I would imagine that others on this list will have some even more
>> elegant and efficient solutions for you, but here's a possibility:
>>
>>  def filt_seq( thing ):
>>    if thing == 38:
>>      thing = thing - 4
>>    elif thing == 40:
>>      thing = thing - 1
>>    return thing
>>
>>  l = [ 1, 17, 12, 38, 4, 40, 17, 19 ]
>>  l = map( filt_seq, l )
>>
>> Good luck,
>
>
> I must have missed a message or two, because I don't understand why  math 
> is being done on constants like that.
> Given my misunderstanding, I'd go with:
>
> my_map = { 38: 34, 40: 39 }
>
> def filter_item(item):
>     return my_map.get(item, item)
>
> l = [ ... ]
> l = map(filter_item, l)

As a list comp:

>>> L=range(30,41)
>>> [{38:34,40:39}.get(n,n) for n in L]
[30, 31, 32, 33, 34, 35, 36, 37, 34, 39, 39]

-Mark