title: cross product between DatetimeIndex and int64
body: <p>I have a pandas <code>DatetimeIndex</code> object <code>dt</code> of length 10k and a list of 10 integers <code>code</code>. I want to create a dataframe of the column cross product (Cartesian product) of the two objects.</p>
  
  <p>How can I do it ?</p>
  
  <pre><code>dt = DatetimeIndex(['2019-01-22 09:00:00', '2019-01-22 09:15:00',
                 '2019-02-07 00:15:00', '2019-02-07 00:30:00',
                 '2019-02-07 00:45:00', '2019-02-07 01:00:00'],
                dtype='datetime64[ns]', length=11137, freq=None)
  
  code = [1000,1001]
  </code></pre>
  
  <p>I wand the DataFrame to be</p>
  
  <pre><code>df
                   datetime        code
          0  '2019-02-07 00:15:00', 1000
          1  '2019-02-07 00:15:00', 1001
          2  '2019-02-07 00:30:00', 1000
                 ....
  </code></pre>