title: Adding keys from dict to columns headers in an existing Pandas dataframe
body: <p>I have a dataframe ('DF1') and I have a dict ('dictdf').
  I want to add columns headers based on the dict, those columns needs to be empty.</p>
  
  <p>DF1:</p>
  
  <pre><code>ID  age
  
  12   33
  23   55
  67   12
  </code></pre>
  
  <p>result:</p>
  
  <pre><code>ID  age  height  eye_color  ....  
  
  12   33    NA      NA       ....
  23   55    NA      NA       ....
  67   12    NA      NA       ....
  </code></pre>
  
  <p>This is what I tried:</p>
  
  <pre><code>colNames = DF1.columns
  for key in dictdf.keys():
      colNames.append(key)
  
  newDF = pd.DataFrame(DF1,columns=colNames)
  </code></pre>
  
  <p>Error:</p>
  
  <pre><code>TypeError: all inputs must be Index
  </code></pre>
  
  <p>Any idea on a simple solution? I don't want to start transforming from dict to DF or the other way around.</p>