Stop-word removal and document tokenization using NLTK library

[Tiger1]

I’m having difficulty eliminating and tokenizing a .text file using nltk. I keep getting the following error message: AttributeError: 'list' object has no attribute 'lower'. I just can’t figure out what I’m doing wrong, although it’s my first time of doing something like this. Below are my lines of code.I’ll appreciate any suggestions, thanks.

Import nltk
from nltk.corpus import stopwords
s = open("C:\zircon\sinbo1.txt").read()
tokens = nltk.word_tokenize(s)
def cleanupDoc(s):
    stopset = set(stopwords.words('english'))
    tokens = nltk.word_tokenize(s)
    cleanup = [token.lower()for token in tokens.lower() not in stopset and  len(token)>2]
    return cleanup
cleanupDoc(s)