Trie Data Structure in Python

trie.py

class Node():
    def __init__(self):
        self.children = {}
        self.last = False
    
    def __str__(self):
        str(self.children.keys())

class Trie():
    def __init__(self):
        self.root = Node()
    
    def insert(self, word):
        current = self.root

        for char in list(word):
            if not char in current.children:
                current.children[char] = Node()
            
            current = current.children[char]

        current.last = True
    
    def search(self, chars):
        current = self.root

        for char in list(chars):
            if not char in current.children:
                return False

            current = current.children[char]

        return True

word = 'casaco'
trie = Trie()

def test_insert():
    trie.insert(word)
    assert trie.root.children['c'] .children['a'].children['s'].children['a'].children['c'].children['o'] != None

def test_search():
    trie.insert(word)

    assert trie.search('casa')
    assert trie.search('cas')
    assert trie.search('casaco')
    assert not trie.search('tonho')
    assert not trie.search('jirimum')