title: numpy.savetxt for 2d array in Python 3.5.1
body: <p>my question is related to <a href="https://stackoverflow.com/questions/35372829/numpy-savetxt-resulting-a-formatting-mismatch-error-in-python-3-5">this</a> but I can't get that solution to work and didn't want to add my own scenario to the old question.</p>
  
  <p>I have a 2D float numpy array, am running python 3.5.1 with numpy 1.10.4, and am trying to write out the array with </p>
  
  <pre><code>numpy.savetext(filename, arrayname, delimiter = ',') 
  </code></pre>
  
  <p>which works beautifully with a 1D array.
  I've tried the solution from the referenced post </p>
  
  <pre><code>with open(filename, 'ab') as f:
      numpy.savetext(f, arrayname, delimiter = ',')
  </code></pre>
  
  <p>to no avail. Actually, I've tried this without the delimiter as well as with 'w', 'wb, 'a'  and with formatting arguments, and always get the same error message:</p>
  
  <pre><code>TypeError: Mismatch between array dtype ('float64') and format specifier.
  </code></pre>
  
  <p>I need to write this 2D array to a file which will be read later into a panda dataframe (have been using read.csv). I understand this may be an issue with numpy.savetxt, so I'm looking for an alternative.</p>