title: Anaconda did not install packages openpyxl and xlrd
body: <p>After installing a new Python 3.6 environment with pandas, numpy, etc. when I tried to use the following pandas method I got the following errors:</p>
  
  <pre><code>&gt;&gt;&gt; df.to_excel(filename)
  ModuleNotFoundError: No module named 'openpyxl'
  </code></pre>
  
  <p>Similar issue occurred earlier when I used the <code>pd.read_excel</code> method.</p>
  
  <p>In both cases the problem was solved by installing <code>openpyxl</code> / <code>xlrd</code> with <code>conda install</code> but I would like to know if this is intentional behaviour and why openpyxl/xlrd wouldn't be considered a dependencies of pandas and installed from the beginning.</p>