title: If iterator is made on some structure to iterate over it using next function
body: <p>For e.g. iterator is created like this:
  <code>Iter1=iter(list)</code>.
  Now this iterator object is created over <code>list</code> and <code>next</code> function will be called</p>
  <p><code>filter()</code> function returns an iterator but this iterator is created over which underlying structure to be iterated upon. The iterator is attached to which kind of data structure in case of <code>filter()</code> function that we used. To which structure iterator is attached to in case of <code>filter()</code> function?</p>