title: Append numpy matrix to binary file without numpy header
body: <p>I continously receive new data as numpy matrices which I need to append to an existing file. Structure and data type of that file are fixed, so I need python to do the conversion for me.</p>
  
  <p>For a single matrix, this works:</p>
  
  <pre><code>myArr = np.reshape(np.arange(15), (3,5))
  myArr.tofile('bin_file.dat')
  </code></pre>
  
  <p>But suppose I'd want to keep appending the existing file with more and more arrays, then <code>numpy.tofile</code> will overwrite any content it finds in the file, instead of appending.</p>
  
  <p>I found that I could also keep doing this:</p>
  
  <pre><code>bfile = open('bin_file.dat', 'ab')
  np.save(bfile, myArr)
  bfile.close()
  </code></pre>
  
  <p>which successfully appends to the binary file. But <code>numpy.save</code> on the other hand does not store the raw binary data, but also saves a header (I assume) which makes the file unreadable by foreign software (I need raw binary with <code>float32</code>).</p>
  
  <p>Reading in the existing content of the file with <code>numpy.fromfile</code>, appending my data and saving it again is not an option, since the file becomes very large and all the I/O would take forever to process.</p>
  
  <p>Is there anything like an <code>append</code> mode for <code>numpy.tofile</code>? Are there other possibilities I am currently missing?</p>