title: initialize pandas DataFrame with defined dtypes
body: <p>The <code>pd.DataFrame</code> docstring specifies a scalar argument for the whole dataframe:</p>
  
  <p><code>dtype : dtype, default None
      Data type to force, otherwise infer</code></p>
  
  <p>Seemingly it is indeed intended to be a scalar, as following leads to an error:</p>
  
  <pre><code>dfbinseq = pd.DataFrame([],
                          columns = ["chr", "centre", "seq_binary"],
                          dtype = ["O", pd.np.int64, "O"])
  
  dfbinseq = pd.DataFrame([],
                          columns = ["chr", "centre", "seq_binary"],
                          dtype = [pd.np.object, pd.np.int64, pd.np.object])
  </code></pre>
  
  <p>The only workaround for creating an empty data frame (which I need to put in a HDF5 store for further <code>append</code>s) for me was</p>
  
  <pre><code>dfbinseq.centre.dtype = np.int64
  </code></pre>
  
  <p>Is there a way to set <code>dtypes</code> arguments at once?</p>