how to extract nested lists? [duplicate]

Question

Duplicates:

• Flattening a shallow list in Python
• Comprehension for flattening a sequence of sequences?

Lets say I have a list with nested lists:

[["a","b","c"], ["d","e","f"], ["g","h","i","j"]...] 

what is the best way to convert it to a single list like that

["a", "b", "c", "d", "e"....] 

Answer 1

Use itertools.chain:

from itertools import chain  list(chain.from_iterable(list_of_lists)) 

Answer 2

There's a straight forward example of this in the itertools documentation (see http://docs.python.org/library/itertools.html#recipes look for flatten()), but it's as simple as:

>>> from itertools import chain >>> list(chain(*x)) ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j'] 

Or, it can be done very easily in a single list comprehension:

>>> x=[["a","b","c"], ["d","e","f"], ["g","h","i","j"]] >>> [j for i in x for j in i] ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j'] 

Or via reduce():

>>> from operator import add >>> reduce(add, x) ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j']