title: pandas dataframe check if index exists in a multi index
body: <p>I have a pandas Dataframe which has a multiindex created using the columns <code>userid</code> and <code>itemid</code>. df looks like this </p>
  
  <pre><code>                  0     1     2
  userid  itemid
  007     5000      9     4     3
  007     4000      6     7     1
  009     3000      1     2     3
  </code></pre>
  
  <p>I want to check if the index [007, 6000] exists in the dataframe df. How can I do that. If I run the following code there is an error <code>TypeError: unhashable type: 'list'</code>. </p>
  
  <pre><code>if [007, 6000] in df.index:
      print('it works')
  </code></pre>