Bisect, is it possible to work with descending sorted lists?

Question

How can I use bisect module on lists that are sorted descending? e.g.

import bisect

x = [1.0,2.0,3.0,4.0] # normal, ascending
bisect.insort(x,2.5)  # -->         


        

Answer 1

Hopefully the "key" argument will be added to bisect module functions one day (see: http://bugs.python.org/issue4356). Unfortunately it's not possible without some kind of workaround at the moment (Python version < 3.4).

One possible workaround is to use a wrapper like:

class ReversedSequenceView(collections.MutableSequence):
    def __init__(self, seq):
        self._seq = seq

    def __getitem__(self, i):
        return self._seq[-1 - i]

    def __setitem__(self, i, v):
        self._seq[-1 - i] = v

    def __delitem__(self, i):
        del self._seq[-1 - i]

    def __len__(self):
        return len(self._seq)

    def insert(self, i, v):
        return self._seq.insert(len(self._seq) - i, v)

Usage:

>>> x = [4., 3., 2., 1.]
>>> bisect.insort(ReversedSequenceView(x), 2.5)
>>> x
[4.0, 3.0, 2.5, 2.0, 1.0]