Python: create sublist without copying

Question

I have a question about how to create a sublist (I hope this is the right term to use) from a given list without copying.

It seems that slicing can create sublists, but

Answer 1

There is no way to do this with built in Python data structures. However, I created a class that does what you need. I don't guarantee it to be bug-free, but it should get you started.

from itertools import islice

class SubLister(object):
    def __init__(self, base=[], start=0, end=None):
        self._base = base
        self._start = start
        self._end = end

    def __len__(self):
        if self._end is None:
            return len(self._base) - self._start
        return self._end - self._start

    def __getitem__(self, index):
        self._check_end_range(index)
        return self._base[index + self._start]

    def __setitem__(self, index, value):
        self._check_end_range(index, "list assignment index out of range")
        self._base[index + self._start] = value

    def __delitem__(self, index):
        self._check_end_range(index, "list assignment index out of range")
        del self._base[index + self._start]

    def __iter__(self):
        return islice(self._base, self._start, self._end)

    def __str__(self):
        return str(self._base[self._start:self._end])

    def __repr__(self):
        return repr(self._base[self._start:self._end])

    # ...etc...

    def get_sublist(self, start=0, end=None):
        return SubLister(base=self._base, start=start, end=end)

    def _check_end_range(self, index, msg="list index out of range"):
        if self._end is not None and index >= self._end - self._start:
            raise IndexError(msg)

Example:

>>> from sublister import SubLister
>>> base = SubLister([1, 2, 3, 4, 5])
>>> a = base.get_sublist(0, 2)
>>> b = base.get_sublist(1)

>>> base
[1, 2, 3, 4, 5]
>>> a
[1, 2]
>>> b
[2, 3, 4, 5]
>>> len(base)
5
>>> len(a)
2
>>> len(b)
4

>>> base[1] = 'ref'
>>> base
[1, 'ref', 3, 4, 5]
>>> a
[1, 'ref']
>>> b
['ref', 3, 4, 5]