title: Appending a matrix to an existing file using numpy
body: <p>I'm trying to add a matrix to an existing csv file. 
  Following <a href="http://mail.scipy.org/pipermail/numpy-discussion/2007-November/030089.html" rel="nofollow">this</a> link, I wrote the following code, </p>
  
  <pre><code>f_handle = file(outfile+'.x.betas','a')
  np.savetxt(f_handle,dataPoint)
  f_handle.close()
  </code></pre>
  
  <p>where I have imported numpy as np, i.e. </p>
  
  <pre><code>import numpy as np
  </code></pre>
  
  <p>But I get this error:</p>
  
  <blockquote>
    <p>f_handle = file(outfile+'.x.betas','a')<br>
    TypeError: 'str' object is not callable</p>
  </blockquote>
  
  <p>I can't figure out what the problem seems to be. 
  Please help :)</p>