title: How to give more weight to Proper Nouns in scikit TfidfVectorizer
body: <p>I am using <code>sci-kit</code>'s <code>TdidfVectorizer</code> to extract keywords from a list of scientific articles. There is an argument for stop_words, but I was wondering if I could give more weight/score to proper nouns such as "Bohr" or "Japan".</p>
  
  <p>Will I have to implement my own custom <code>tfidf vectorizer</code> or can I still use this built in one?</p>
  
  <pre><code>tf = TfidfVectorizer(strip_accents='ascii', 
                       analyzer='word',
                       ngram_range=(1,1),
                       min_df = 0,
                       stop_words = stopwords,
                       lowercase = True)
  </code></pre>