What is the fastest way to flatten arbitrarily nested lists in Python? [duplicate]

Question

Possible Duplicate:
Flattening a shallow list in Python
Flatten (an irregular) list of lists in Python

EDIT: The question is not how to do it - this has been discussed in other questions - the question is, which is the fastest method?

I've found solutions before, but I'm wondering what the fastest solution is to flatten lists which contain other lists of arbitrary length.

For example:

[1, 2, [3, 4, [5],[]], [6]] 

Would become:

[1,2,3,4,5,6] 

There can be infinitely many levels. Some of the list objects can be strings, which mustn't be flattened into their sequential characters in the output list.

Answer 1

Here's a recursive approach that is string friendly:

nests = [1, 2, [3, 4, [5],['hi']], [6, [[[7, 'hello']]]]]  def flatten(container):     for i in container:         if isinstance(i, (list,tuple)):             for j in flatten(i):                 yield j         else:             yield i  print list(flatten(nests)) 

returns:

[1, 2, 3, 4, 5, 'hi', 6, 7, 'hello'] 

Note, this doesn't make any guarantees for speed or overhead use, but illustrates a recursive solution that hopefully will be helpful.