title: Why is 'key' an unexpected keyword of sort_values()
body: <p>I am trying to implement the code</p>
  <pre><code>sort_order = {
  'Documentary':0,
  'Film-Noir':1,
  'Biography':2,
  'History':3,
  'War':4,
  'News':5,
  'Animation':6,
  'Musical':7,
  'Music':8,
  'Drama':9
  }
  
  df.sort_values(by=['genre'], key=lambda x: x.map(sort_order))
  </code></pre>
  <p>But I receive this error:</p>
  <pre><code>TypeError: sort_values() got an unexpected keyword argument 'key'
  </code></pre>
  <p>I downloaded the latest version of Pandas to try and fix this using conda update pandas but this did not change anything. I know something is going wrong because their page <a href="https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.DataFrame.sort_values.html" rel="nofollow noreferrer">here</a> shows that key should be recognized.</p>
  <p>Any help would be greatly appreciated.</p>