在Python中打印列表的非递归方式

Question

有没有办法以非递归方式执行以下操作：

my_list = [
    "level 1-1",
    "level 1-2",
    "level 1-3",
        [
            "level 2-1",
            "level 2-2",
            "level 2-3",
            [
                "level 3-1",
                "level 3-2"
            ]
        ],
    "level 1-4",
    "level 1-5"
    ]


def print_list(the_list, indent_level=0):
    for item in the_list:
        if isinstance(item, list):
            print_list(item, indent_level + 1)
        else:
            print "\t" * indent_level, item


print_list(my_list)

Answer 1

stack = [(my_list, -1)]
while stack:
    item, level = stack.pop()

    if isinstance(item, list):
        for i in reversed(item):
            stack.append((i, level+1))
    else:
        print "\t" * level, item

Answer 2

def print_list(the_list, indent_level=0):
    stack = [iter(the_list)]
    while stack:
        try:
            item = stack[-1].next()
        except StopIteration:
            stack.pop()
            indent_level -= 1
            continue
        if isinstance(item, list):
            indent_level += 1
            stack.append(iter(item))
        else:
            print "\t" * indent_level, item

Answer 3

这是Martin Löwis版本的一个变体，它使用for/else代替手动捕获StopIteration，使用len(stack)代替跟踪缩进级别。

def print_list(the_list):
    stack = [iter(the_list)]
    while stack:
        for item in stack[-1]:
            if isinstance(item, (list, tuple)):
                stack.append(iter(item))
                break
            else:
                print '\t' * (len(stack)-1), item
        else:
            stack.pop()