Suggestion for impriving list comprehensions
Steven D. Majewski
sdm7g at Virginia.EDU
Fri Jul 27 03:20:54 CEST 2001
On 26 Jul 2001, Thomas Bellman wrote:
> or my personal favourite
>
> map(lambda x,g=fib(): g.next(), range(N))
>
Cool.
I see I can get the odd values from the first 10 fibonacci numbers with:
>>> def odd(x): return x % 2
...
>>> def even(x) : return not(odd(x))
...
>>> filter( odd, map( lambda n,f=fib().next: f(), range(10) ))
[1, 1, 3, 5, 13, 21, 55]
But the first 10 odd fibonacci numbers doesn't work the same way.
But Re: Guido's suggestion about an iterator algebra :
maybe what we need are iterator versions of map, filter, reduce, etc.
Given:
>>> def gfilter( f, s ):
... for x in s:
... if f(x): yield x
Then the first 10 odd fibonacci numbers are:
>>> map( lambda n,f=gfilter( odd, fib() ).next: f(), range(10) )
[1, 1, 3, 5, 13, 21, 55, 89, 233, 377]
( I'm not completely sure that I actually *like* all the iterator
syntax and semantics -- the extra indirection which sometimes
needs to be explicit ( the "next" attribute ) but sometimes
gets done automagically by 'for' is something I'm not quite
used to yet! )
-- Steve Majewski
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