title: Save / load scipy sparse csr_matrix in portable data format
body: <p>How do you save/load a scipy sparse <code>csr_matrix</code> in a portable format?  The scipy sparse matrix is created on Python 3 (Windows 64-bit) to run on Python 2 (Linux 64-bit).  Initially, I used pickle (with protocol=2 and fix_imports=True) but this didn't work going from Python 3.2.2 (Windows 64-bit) to Python 2.7.2 (Windows 32-bit) and got the error:</p>
  
  <pre><code>TypeError: ('data type not understood', &lt;built-in function _reconstruct&gt;, (&lt;type 'numpy.ndarray'&gt;, (0,), '[98]')).
  </code></pre>
  
  <p>Next, tried <code>numpy.save</code> and <code>numpy.load</code> as well as <code>scipy.io.mmwrite()</code> and <code>scipy.io.mmread()</code> and none of these methods worked either.</p>