Initializing a list with copies

[Ralf Juengling]

billdozier at hotmail.com (Bill Dozier) writes:

> Ralf Juengling <juenglin at informatik.uni-freiburg.de> wrote in message news:<xduy9fa4z2x.fsf at leto.informatik.uni-freiburg.de>...
> 
> 
> 
> This looks like the old "mutable initializer" thingie.
> 

yeah probably old traps, newbies are falling into in any season.


> > >>> l = [[] for i in range(n)]
> 
> > Can this be done more elegant? 
> "[[] for i in range(n)]" looks fine to me.
> 
> > By some expression that was similar to '[[]]*n' ? 
> Do you mean, "with few characters to type?" That's not the same as
> "with more elegance."

That's admittedly a bit finical, but I don't like to have to create a
temporary list to create the list l. That's why it looks unelegant to
me. (Okay, I could use 'xrange' instead of 'range'...)

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?

Ralf