Path: csiph.com!fu-berlin.de!uni-berlin.de!not-for-mail
From: srinivas devaki <mr.eightnoteight@gmail.com>
Newsgroups: comp.lang.python
Subject: Re: How To Create A Endles List Of Lists In Python...???
Date: Fri, 20 Nov 2015 23:58:20 +0530
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On Fri, Nov 20, 2015 at 6:39 PM, Chris Angelico <rosuav@gmail.com> wrote:
> My crystal ball suggests that defaultdict(list) might be useful here.
>
> ChrisA

I used something similar to this for some problem in hackerrank,
anyway i think this is what you want.

class defaultlist(object):
    def __init__(self, factory, data=None):
        self.factory = factory
        self.list = []
        self.data = data

    def __getitem__(self, x):
        if x >= len(self.list):
            self.list.extend([self.factory() for _ in
range(len(self.list), x + 1)])
        return self.list[x]

    def __repr__(self):
        return str(self)

    def __str__(self):
        if len(self.list) == 0:
            return '(' + str(self.data) +  ')[...]'
        return ''.join(['(', str(self.data), ')['] + map(str,
self.list) + [', ...]'])


    def __setitem__(self, x, v):
        if x >= len(self.list):
            self.list.extend([self.factory() for _ in
range(len(self.list), x + 1)])
        self.list[x] = v

def main():
    factory = lambda: defaultlist(factory)
    list_of_lists = defaultlist(factory)
    print (list_of_lists[0])
    list_of_lists[0][10].data = 20
    print (list_of_lists[0])


main()

Gist: https://gist.github.com/c0c2ee1e7c6535ef8c3d