title: Add and remove words from the NLTK stopwords list
body: <p>I'm trying to add and remove words from the NLTK stopwords list:</p>
  
  <pre><code>from nltk.corpus import stopwords
  
  stop_words = set(stopwords.words('french'))
  
  #add words that aren't in the NLTK stopwords list
  new_stopwords = ['cette', 'les', 'cet']
  new_stopwords_list = set(stop_words.extend(new_stopwords))
  
  #remove words that are in NLTK stopwords list
  not_stopwords = {'n', 'pas', 'ne'} 
  final_stop_words = set([word for word in new_stopwords_list if word not in not_stopwords])
  
  print(final_stop_words)
  </code></pre>
  
  <p>Output:</p>
  
  <pre><code>Traceback (most recent call last):
    File "test_stop.py", line 10, in &lt;module&gt;
  new_stopwords_list = set(stop_words.extend(new_stopwords))
  AttributeError: 'set' object has no attribute 'extend'
  </code></pre>