title: numpy.r_ is not a function. What is it?
body: <p>According to the numpy/scipy doc on <code>numpy.r_</code> <a href="http://docs.scipy.org/doc/numpy/reference/generated/numpy.r_.html">here</a>, it is "not a function, so takes no parameters".</p>
  
  <p>If it is not a function, what is the proper term for "functions" such as <code>numpy.r_</code>?</p>