getting all elements of a python list ,including sublists

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Flatten (an irregular) list of lists in Python

I have a python list whose elements can be letters or lists of letters.I wanted to write a function to extract all elements as below

suppose

l=['a',['b',['c']] ]

The output need to be ['a','b','c']

I thought recursion would be the correct way to do this. The base case may be that the list contains only one element. I tried to code this..but the output is

['a', 'b', ['c']]

Can someone please tell me what went wrong here?

def get_all_elements(mylist):
    if len(mylist)==1:
        return mylist[0]
    else:
        output=[mylist[0]]
        output+=get_all_elements(mylist[1:])
        return output

Are they always single letters? – mgilson Oct 19 '12 at 15:00 — mgilson, Oct 19 '12 at 15:00
are the lists nested arbitrarily deep, or 3 deep at max? – Mike Corcoran Oct 19 '12 at 15:00 — Mike Corcoran, Oct 19 '12 at 15:00

mgilson · Accepted Answer · 2012-10-19T15:09:16.517

This seems to work Ok:

def flatten(iterable):
   out = []
   for i in iterable:
      if hasattr(i,'__iter__'):
         out.extend(flatten(i))
      else:
         out.append(i)
   return out

l=['a',['b',['c']] ]   
print flatten(l)

Where you went wrong is that in your solution, mylist[0] can itself be a list (of length 1) which contains another list (of arbitrary length). In that case, you just returned it.

score 1 · Answer 2 · edited May 23 '17 at 12:02

1

When you check to see if mylist is of length 1, you don't check for the case where its contents are a list. Here's an example that will highlight your problem.

get_all_elements([1, [2, [3, 4]]])

If you want a complete solution, Flattening a shallow list in Python and Comprehension for flattening a sequence of sequences? are good places to look.

edited May 23 '17 at 12:02

Community

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answered Oct 19 '12 at 15:01

nmichaels

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score 0 · Answer 3 · answered Oct 19 '12 at 15:03

0

this will work on up to 3 levels deep, if the depth is arbitrary i don't think you'll be able to use a list comprehension.

[grandchild for parent in l for child in parent for grandchild in child]

answered Oct 19 '12 at 15:03

Mike Corcoran

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getting all elements of a python list ,including sublists

3 Answers3