Simple implementation of trie data structure, O(n) for finding words

trie.py

class Trie:
   def __init__(self):
       self.trie = dict()

   def insert(self, key, value):
       p = self.trie
       for c in key:
           if c not in p: p[c] = dict()
           p = p[c]
       p[None] = value

   def find(self, key):
       p = self.trie
       for c in key:
           if c not in p: raise KeyError
           p = p[c]
       if None not in p: raise KeyError
       return p[None]