gistfile1.py

s = {
        'tag': '<span class="boom"></span>',
        'content':
        [
            'Server status: ',
            {
                'tag': '<a></a>',
                'content':
                [
                    '[online]',
                    {
                        'tag': '<b></b>',
                        'content': ['!!!']
                    }
                ]
            },
            '<br>',
            {
                'tag': '<span class="foo"></span>',
                'content': ['Done']
            }
        ]
    }

class node(object):
    def __init__(self, line):
        t = line['tag'].find('><') + 1
        self.open_tag = line['tag'][:t]
        self.close_tag = line['tag'][t:]
        self._content = line['content']
        self.current_pos = 0
        self.chars_out = 0

    def process(self):
        content = ''
        n = 0
        for part in self._content:
            if n < self.current_pos:
                if type(part) == str:
                    sub_content = part[:self.current_pos - n]
                    content += sub_content
                    n += len(sub_content)
                else:
                    child = node(part)
                    child.current_pos = self.current_pos - n
                    content += child.process()
                    n += child.chars_out
        self.chars_out = n
        return self.open_tag + content + self.close_tag

    def __len__(self):
        foo = lambda c: sum(len(x) if type(x) is str else foo(x['content']) for x in c)
        return foo(self._content)

def main():
    n = node(s)
    for t in xrange(len(n)):
        print n.process()
        n.current_pos += 1
    print n.process()

if __name__ == "__main__":
    main()