Split a list into parts based on a set of indexes in Python

What is the best way to split a list into parts based on an arbitrary number of indexes? E.g. given the code below

indexes = [5, 12, 17]
list = range(20)

return something like this

part1 = list[:5]
part2 = list[5:12]
part3 = list[12:17]
part4 = list[17:]

If there are no indexes it should return the entire list.

This is the simplest and most pythonic solution I can think of:

def partition(alist, indices):
    return [alist[i:j] for i, j in zip([0]+indices, indices+[None])]

if the inputs are very large, then the iterators solution should be more convenient:

from itertools import izip, chain
def partition(alist, indices):
    pairs = izip(chain([0], indices), chain(indices, [None]))
    return (alist[i:j] for i, j in pairs)

and of course, the very, very lazy guy solution (if you don't mind to get arrays instead of lists, but anyway you can always revert them to lists):

import numpy
partition = numpy.split

I would be interested in seeing a more Pythonic way of doing this also. But this is a crappy solution. You need to add a checking for an empty index list.

Something along the lines of:

indexes = [5, 12, 17]
list = range(20)

output = []
prev = 0

for index in indexes:
    output.append(list[prev:index])
    prev = index

output.append(list[indexes[-1]:])

print output

produces

[[0, 1, 2, 3, 4], [5, 6, 7, 8, 9, 10, 11], [12, 13, 14, 15, 16], [17, 18, 19]]

My solution is similar to Il-Bhima's.

>>> def parts(list_, indices):
...     indices = [0]+indices+[len(list_)]
...     return [list_[v:indices[k+1]] for k, v in enumerate(indices[:-1])]

Alternative approach

If you're willing to slightly change the way you input indices, from absolute indices to relative (that is, from [5, 12, 17] to [5, 7, 5], the below will also give you the desired output, while it doesn't create intermediary lists.

>>> from itertools import islice
>>> def parts(list_, indices):
...     i = iter(list_)
...     return [list(islice(i, n)) for n in chain(indices, [None])]