Word ladder solver exercise

ladder.py

#!/usr/bin/env python3

from sys import argv
from collections import deque, defaultdict

DICTFILE = "/usr/share/dict/words"

def get_words(length):
    words = []
    with open(DICTFILE, 'r') as dictfile:
        for i in dictfile:
            i = i.strip()
            if len(i) == length and i.isalpha() and i.islower():
                words.append(i)
    return words

def diffcount(s,t):
    count = 0
    for x,y in zip(s, t):
        if x != y:
            count += 1
    return count

def find_shortest_path(graph, start, end):
        dist = {start: [start]}
        q = deque([start])
        while len(q):
            at = q.popleft()
            for next in graph[at]:
                if next not in dist:
                    dist[next] = [dist[at], next]
                    q.append(next)
        return flatten_result(dist.get(end))

def flatten_result(result):
    while isinstance(result[0], list):
        result = result[0] + result[1:]
    return result

def main():
    start = argv[1]
    end = argv[2]
    graph = defaultdict(lambda: [])
    if len(start) != len(end):
        print(f"{start}({len(start)}) and {end}({len(end)}) are not the same "
            "length!")
        return
    wordlist = get_words(len(start))
    if start not in wordlist:
        print(f"{start} is not a word")
        return
    if end not in wordlist:
        print(f"{end} is not a word")
        return

    graph[start] = [w for w in wordlist if diffcount(w, start) == 1]
    fail = False
    while not fail:
        fail = True
        for k,v in [*graph.items()]:
            for word in v:
                if word not in graph:
                    fail = False
                    graph[word] = [w for w in wordlist if diffcount(w, word) == 1]
                    if end in graph[word]:
                        print()
                        path = find_shortest_path(graph, start, end)
                        if path:
                            print(' -> '.join(path))
                            return
                        else:
                            fail = True
    print("No path found")

if __name__ == '__main__':
    main()