Question

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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

Answer 1

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.