nltk Lemmatizer TypeError: unhashable type: 'list'

Question

import nltk
from nltk.stem import WordNetLemmatizer
lemmatizer = nltk.WordNetLemmatizer()
import self as self

intents = json.loads(open('intents.json').read())

words = []
classes = []
documents = []
ignore_letters = ['?', '!', '.', ',', '~']

lemmatizer = WordNetLemmatizer

words = [lemmatizer.lemmatize(self, word) for word in words if word and word not in ignore_letters]
words = sorted(set(words))

print("words")

When I run my code, TypeError: unhashable type: 'list' will show. I don't know how to solve this error please help. Thank you.