title: In Python, does this expression "(a is b) == ( id(a) == id(b) )" always return True?
body: <p>In Python, the expression <code>(a is b) == ( id(a) == id(b) )</code> appears to always returns True, where <code>a</code> and <code>b</code> are variables referring to some object, since the <code>id</code> function returns the memory where they are stored and <code>is</code> is used for object identity.</p>
  
  <p>Are there any exceptions?</p>