Simple tries implementation in python

tries.py

#!/usr/bin/env python3

class Node(dict):

    def __init__(self, *args, **kwargs):
        super(*args, **kwargs)
        self.end = kwargs.get('end', False)

    def add_word(self, word):
        if not word:
            self.end = True
            return

        if word[0] not in self:
            self[word[0]] = Node()

        self[word[0]].add_word(word[1:])

    def find_word(self, word):
        if not word:
            return self.end
        if word[0] in self:
            return self[word[0]].find_word(word[1:])
        return False

    def get_all_words(self):
        if self.end:
            return [""]
        result = []
        for char, node in self.items():
            result.extend([char + x for x in node.get_all_words()])
        return result

    def __str__(self):
        result = ""
        alphabetical = [char for char in self]
        alphabetical.sort()
        for char in alphabetical:
            result += "['{}': {}{}]".format(char, str(self[char]), "." if self[char].end else "")
        return result


if __name__ == '__main__':
    t = Node()
    t.add_word('ace')
    t.add_word('actor')
    t.add_word('brie')

    assert str(t) == "['a': ['c': ['e': .]['t': ['o': ['r': .]]]]]['b': ['r': ['i': ['e': .]]]]"

    assert t.find_word('') == False
    assert t.find_word('ac') == False
    assert t.find_word('ace') == True
    assert t.find_word('actor') == True
    assert t.find_word('acclaim') == False
    assert t.find_word('brieyonce') == False
    assert t.find_word('brie') == True

    assert len(t) == 2
    assert len(t['a']) == 1
    assert len(t['a']['c']) == 2

    assert set(t.get_all_words()) == set(['actor', 'ace', 'brie'])