Parse and spin spin-formatted article

spin.py

import random


# Usage: parse(text).spin()

class Node:
    def __init__(self):
        None

    def spin(self):
        raise Exception('Not implemented')


class ListNode(Node):
    def __init__(self, nodes=[]):
        self.nodes = nodes

    def spin(self):
        text = ''
        for node in self.nodes:
            text = text + node.spin()
        return text

    def append_node(self, node):
        if isinstance(node, ListNode):
            for n in node.nodes:
                self.nodes = [n] + self.nodes
        else:
            self.nodes = [node] + self.nodes

    def __repr__(self):
        return '[' + ','.join([
                str(n) for n in self.nodes
                ]) + ']'


class ChoiceNode(Node):
    def __init__(self, choices=[]):
        self.choices = choices

    def choose(self):
        if len(self.choices) > 0:
            return random.choice(self.choices)
        else:
            return None

    def spin(self):
        choice = self.choose()
        if choice is not None:
            return choice.spin()
        else:
            return ''

    def add_choice(self, choice):
        self.choices.append(choice)

    def __repr__(self):
        return '{' + '|'.join([
                str(c) for c in self.choices
                ]) + '}'


class TextNode(Node):
    def __init__(self, text=''):
        self.text = text

    def spin(self):
        return self.text

    def add_char(self, c):
        self.text = self.text + c

    def __repr__(self):
        return '(' + self.text + ')'


def parse(text):
    stack = []
    for c in text:
        if c == '{':
            start_choice(stack)
        elif c == '|':
            add_choice(stack)
        elif c == '}':
            end_choices(stack)
        else:
            # normal char
            push_text(stack, c)
    return ListNode(nodes=stack)


def start_choice(stack):
    stack.append('{')


def add_choice(stack):
    stack.append('|')


def end_choices(stack):
    branch = ListNode(nodes=[])
    choices = ChoiceNode(choices=[])
    while True:
        top = stack.pop()
        if top == '|':
            choices.add_choice(branch)
            branch = ListNode(nodes=[])
        elif top == '{':
            choices.add_choice(branch)
            stack.append(choices)
            return
        else:
            branch.append_node(top)


def push_text(stack, c):
    if len(stack) > 0:
        if isinstance(stack[-1], TextNode):
            stack[-1].add_char(c)
            return
    stack.append(TextNode(c))


def test():
    f = open('sample.txt', 'r')
    text = f.read()
    print parse(text).spin()
    # text = '''{{a|b}|c}'''
    # sa = parse(text)
    # article = sample()
    # print article.spin()


parse_article = parse


if __name__ == '__main__':
    test()