title: Python: what difference between 'is' and '=='?
body: <p>I'm trying next code:</p>
  
  <pre><code>x = 'asd'
  y = 'asd'
  z = input() #write here string 'asd'. For Python 2.x use raw_input()
  x == y # True.
  x is y # True.
  x == z # True.
  x is z # False.
  </code></pre>
  
  <p>Why we have false in last expression?</p>