title: how to use functions from a sub-module
body: <p>I am confused about how to use functions from a sub module. For example, <code>numpy</code> has a submodule <code>linalg</code>, which contains a function <code>solve</code>, so I can do:</p>
  
  <pre><code>import numpy as np
  np.linalg.solve(  # And then specify what I want to solve
  </code></pre>
  
  <p>Similarly, <code>scipy</code> has a subpackage <code>sparse</code>, which has a subpackage <code>linalg</code>, which has a function <code>spsolve</code>, yet I cannot do this:</p>
  
  <pre><code>import scipy.sparse as sp
  sp.linalg.spsolve( # And then whatever I want to solve
  </code></pre>
  
  <p>Why not? Shouldn't that work?</p>