Anagram

[Joseph A Knapka]

Alex Martelli wrote:
> 
> "Joseph A Knapka" <jknapka at earthlink.net> wrote in message
> news:3C4ED1A5.56CE7B60 at earthlink.net...
>     ...
> > # This one allows you to pick an anagram from anywhere
> > # in the sequence. <Ana> is the index of the anagram to
> > # pick from the possible anagrams of <lis>.
> > def pickana(lis,ana):
> >     if not lis:
> >         return []
> >     idx1 = int(ana/fact(len(lis)-1))
> >     which1 = lis[idx1]
> >
> >     # Still annoying. Can I "comprehend" this somehow?
> >     llis = lis[:]
> >     del llis[idx1]
> 
> Not sure what you mean.  "get the idx1-th element
> from list llis and remove it from the list too"
> is llis.pop(idx1); is that what you mean by
> "comprehend"?

As Mr Hogg rightly inferred, what annoys me is having
to first make a copy of "lis" and then remove the chosen
element. I wanted to something like:

llis = [some comprehension yielding lis-<the chosen index>]

but, I wanted it, y'know, comprehensible...
 
> >     rest = pickana(llis,ana%fact(len(lis)-1))
> >     return [which1] + rest
> 
> Or, non-recursively...:
> 
> def pickanagram(lis, anaind):
>     result = []
>     llis = lis[:]
>     while llis:
>         anaind, indx = divmod(anaind, len(llis))
>         result.append(llis.pop(indx))
>     return result
> 
> I don't think the fact() calls in your pickana are
> correct -- I think you need a divmod(ana,len(lis))
> in your version too (or equivalently separate uses
> of operators / and % as you have, but divmod seems
> clearer to me in this case).

My version gives the correct results. We are counting
anagrams from opposite directions, more or less -
I'm chopping off high-order bits to choose list
indices, and you're chopping off low-order ones.
Your way is clearly better :-) It didn't occur to
me until I read your code that with this kind of
enumeration argument, it doesn't matter in which
direction you consume the index value.
 
> pickanagram seems nice & readable, but if squeezing
> functionality into fewer statements were the goal,
> something might be feasible.  Usual disclaimers: I
> am *NOT* advocating the following as good, or even
> halfway sensible, Python programming, just playing
> with Joe's "challenge":-).

Yeah, right. Denial is the first sign...
 
> Basically, the body of pickanagram is CLOSE to a list
> comprehension (a single statement) plus the copy of
> lis (to make pickanagram nondestructive on its argument!);
> this suggests we need to check if we CAN indeed make it
> into a list-comprehension.

{insanity snipped}

Ow, Ow OW! That hurt my brain... and it felt goooood....

Cheers,

-- Joe
"I should like to close this book by sticking out any part of my neck
 which is not yet exposed, and making a few predictions about how the
 problem of quantum gravity will in the end be solved."
 --- Physicist Lee Smolin, "Three Roads to Quantum Gravity"