title: Python slice how-to, I know the Python slice but how can I use built-in slice object for it?
body: <p>What's the use of built-in function <code>slice</code> and how can I use it?<br>
  The direct way of Pythonic slicing I know - <code>l1[start:stop:step]</code>. I want to know if I have a slice object, then how do I use it?</p>