Python如何拉平（flatten）嵌套列表(nested list)

有时候会用到嵌套的列表(list)，比如

[1, 2, [3, 4, [5, 6]], ["abc", "def"]]  

 如果将嵌套的列表拉平（flatten）呢？变成：

[1, 2, 3, 4, 5, 6, "abc", "def"]  

方法有很多，目前了解到的各方面都比较好，也很pythonic的方法是：

def flatten(l):      for el in l:          if hasattr(el, "__iter__") and not isinstance(el, basestring):              for sub in flatten(el):                  yield sub          else:              yield el  

l = [1, 2, [3, 4, [5, 6]], ["abc", "def"]]  l2 = [x for x in flatten(l)]  print l2  #[1, 2, 3, 4, 5, 6, "abc", "def"]