def remove_stopwords(tokens):

    """
    This function takes in a list of tokens (from the 'preprocess' function) and 
    removes a list of stopwords. Custom stopwords can be added to the 'custom_stopwords' list.
    """

    #set default and custom stopwords
    stop_words = nltk.corpus.stopwords.words('english')
    custom_stopwords = []
    stop_words.extend(custom_stopwords)

    #filter out stopwords
    filtered_tokens = [word for word in tokens if word not in stop_words]

    return(filtered_tokens)