Initializing a list with copies

[Duncan Booth]

Ralf Juengling <juenglin at informatik.uni-freiburg.de> wrote in 
news:xduu1pt1iuf.fsf at leto.informatik.uni-freiburg.de:

> Here's a proposal, that is 'more elegant' in my eyes. If the builtin 
> 'list' type was an *iterable* factory function and we'd borrow the 
> function 'take' from a more functional language, say
> 
> def take(n, i):
>     if not n:
>         return []
>     else:
>         i = iter(i)
>         return [i.next()] + take(n-1, i)
> 
> then 
> 
> l = take(n, list)
> 
> would do it.
> 
> BTW: It is not easy to add __iter__ to list's meta-type, is it?

How about writing a generator to give you a list of any type:?

def listof(sometype=list):
    while 1: yield sometype()

def take(n, i):
    i = iter(i)
    return [ i.next() for j in range(n) ]

take(6, listof(list))
take(99, listof(dict))

It occurs to me that it ought to be possible to produce a type 
(pseudolist/lazylist?) that can be constructed from a sequence and has all 
the methods of a list, but which only accesses the argument sequence when 
it absolutely has to. e.g.:

    lst1 = lazylist(listof())[:6]
    lst2 = lazylist(file(name))[10:20]

-- 
Duncan Booth                                             duncan at rcp.co.uk
int month(char *p){return(124864/((p[0]+p[1]-p[2]&0x1f)+1)%12)["\5\x8\3"
"\6\7\xb\1\x9\xa\2\0\4"];} // Who said my code was obscure?