Path: csiph.com!usenet.pasdenom.info!news.etla.org!news.stack.nl!newsfeed.xs4all.nl!newsfeed2.news.xs4all.nl!xs4all!newsgate.cistron.nl!newsgate.news.xs4all.nl!post.news.xs4all.nl!not-for-mail
To: python-list@python.org
From: "Frank Millman" <frank@chagford.com>
Subject: Re: Creating a list with holes
Date: Sat, 4 Jan 2014 09:00:22 +0200
References: <CACwCsY5P47-dB1NLQTUTQ=0aF6B+-M3y4hCxcUGmcVmHM8=-xQ@mail.gmail.com>
Precedence: list
Newsgroups: comp.lang.python
Message-ID: <mailman.4894.1388818829.18130.python-list@python.org>
Lines: 47
NNTP-Posting-Host: 2001:888:2000:d::a6
Xref: csiph.com comp.lang.python:63114


"Larry Martell" <larry.martell@gmail.com> wrote in message 
news:CACwCsY5P47-dB1NLQTUTQ=0aF6B+-M3y4hCxcUGmcVmHM8=-xQ@mail.gmail.com...
>I think I know the answer is no, but is there any package that allows
> creating a list with holes in it? E.g. I'd want to do something like:
>
> x[10] = 12
> x[20] = 30
>
> I'm thinking of something like defaultdict but for lists (I know
> that's very different, but ... )
>
> Thanks!
> -larry

Just out of interest, I asked the same question on this list many years ago, 
and someone actually gave me an answer. It was something like the 
following -

>>> class MyList(list):
...     def __getitem__(self, pos):
...         try:
...             return list.__getitem__(self, pos)
...         except IndexError:
...             return None
...     def __setitem__(self, pos, value):
...         try:
...             list.__setitem__(self, pos, value)
...         except IndexError:
...             diff = pos - list.__len__(self)
...             self.extend([None] * diff)
...             self.append(value)
...
>>> ml = MyList()
>>> ml[3]
>>> ml[3] = 'a'
>>> ml
[None, None, None, 'a']
>>>

I wanted it because I was familiar with it from a previous language I had 
used. As is turns out, I never actually used it, but I was impressed!

Frank Millman