List Flatten

flat_list.py

import collections
alist = [[1, 2, [3, [5, 6, 7]]], 4]


def flat_list(xs):
    for x in xs:
      if isinstance(x, str) or not isinstance(x, collections.Iterable):
          yield x
      else:
          yield from flat_list(x)


print(list(flat_list(alist)))

assert list(flat_list(alist)) == [1, 2, 3, 5, 6, 7, 4]
assert list(flat_list([1, 2, 3, 4, 5])) == [1, 2, 3, 4, 5]
assert list(flat_list((1, 3, 5, [4, 5, 6, 'a']))) == [1, 3, 5, 4, 5, 6, 'a']