adding elements of a list of lists

Question

A function named add_r that takes a list as argument and adds all numeric values in all levels of the provided list. Assume that the input list will always be a list of numbers or sub-lists that may contain further sub-lists and/or numbers. For example, add_r( [[1, 2], [3], [[4, 5, 6], [7, 8, [9, 10]]]]) should return 55. Take into account that the input list provided as argument to the function can contain sublists at any depth.

another homework assignment. Can't get any more blatant than this — iruvar, Jul 12 '13 at 05:19

Ashwini Chaudhary · Answer 1 · 2013-07-12T05:20:25.353

2

Use a recursive function:

from collections import Iterable
def add_r(lis):
     for x in lis:
         if isinstance(x, Iterable):
             for y in add_r(x):
                 yield y
         else:        
             yield x

>>> lis = [[1, 2], [3], [[4, 5, 6], [7, 8, [9, 10]]]]
>>> sum(add_r(lis))
55

On py2.x you can also use compiler.ast.flatten:

>>> from compiler.ast import flatten
>>> sum(flatten(lis))
55

edited Jul 12 '13 at 05:20

answered Jul 12 '13 at 05:12

Ashwini Chaudhary

232,417
55
437
487

+1 for using the flatten function . – tusharmakkar08 Jul 12 '13 at 05:25
I think `if isinstance(x, Iterable) and not isinstance(x, str)` is more general though here there is only int. – zhangyangyu Jul 12 '13 at 05:38
@zhangyangyu If list contains non-numeric values then `sum()` will raise an error too, so no need to handle strings here. – Ashwini Chaudhary Jul 12 '13 at 05:41
Yeah, it is my fault. @AshwiniChaudhary – zhangyangyu Jul 12 '13 at 05:42

adding elements of a list of lists

1 Answers1