如何将一个多重嵌套列表附加到一个空列表中？

Question

I've seen this code in a book:

def print_loop(items):
    for i in items: 
        if isinstance(i, list):
            print_loop(i)
        else:
            print(i)

What this does is it prints out a multiply nested list. Works perfectly fine with any multiply layered list.

I thought how about if we modify the function so that it simply appends the multiply nested list to an empty list. Here is how I changed it:

def append_loop(items):
    func_items = []

    for i in items: 
        if isinstance(i, list):
            append_loop(i)
        else:
            func_items.append(i)
    return func_items

If I have a list like: items = [1,2,3 [4,5, [6,7]]] and try with with my function, all it return is [1,2,3].

Answer 1

When you call append_loop(i) , this is returning a flattened list. You have to do something with that, for instance extending func_items with it:

>>> def append_loop(items):
...   func_items = []
...   for i in items:
...       if isinstance(i, list):
...           func_items.extend(append_loop(i))
...       else:
...           func_items.append(i)
...   return func_items
...
>>> append_loop([1,2,[3,[4,5]]])
[1, 2, 3, 4, 5]

Otherwise, you could use a global list:

>>> global_func_items = []
>>> def append_loop2(items):
...   for i in items:
...       if isinstance(i, list):
...           append_loop2(i)
...       else:
...           global_func_items.append(i)
...
>>> append_loop2([1,2,[3,[4,5]]])
>>> print global_func_items
[1, 2, 3, 4, 5]