title: Lemmatize a doc with spacy?
body: <p>I have a spaCy <code>doc</code> that I would like to lemmatize.</p>
  
  <p>For example:</p>
  
  <pre><code>import spacy
  nlp = spacy.load('en_core_web_lg')
  
  my_str = 'Python is the greatest language in the world'
  doc = nlp(my_str)
  </code></pre>
  
  <p>How can I convert every token in the <code>doc</code> to its lemma?</p>