import os
import re

def past_verb(word):
    suffix = "ed"
    path = "./rules.txt"
    rules = {}

    if os.path.isfile(path):
        f = open(path)
        words = f.read()
        words = words.split()
    else:
        return "rules.txt をダウンロードしてpast_verb.pyと同じフォルダに格納して下さい"

    for i in words:
        tmp = i.split(",")
        rules[tmp[0]] = tmp[1]

    if word in norules:
        suffix = ""
        word = rules[word]
    elif word[-1] == "e":
        suffix = "d"
    elif word[-1] == "p":
        suffix = word[-1] + suffix
    elif word[-1] == "y":
        word = word[:-1] + "i"

    res = word + suffix
    return res