title: Why does numpy.r_ use brackets instead of parentheses?
body: <p>Numpy.r_, .c_ and .s_ are the only Python functions I've come across that take arguments in square brackets rather than parentheses. Why is this the case? Is there something special about these functions? Can I make my own functions that use brackets (not that I want to; just curious)?</p>
  
  <p>For example, the proper syntax is:</p>
  
  <pre><code>    np.r_['0,2', [1,2,3], [4,5,6]]
  </code></pre>
  
  <p>I would have expected it to be:</p>
  
  <pre><code>    np.r_('0,2', [1,2,3], [4,5,6])
  </code></pre>