title: Why 'is' return different result for 'same compare' in Python?
body: <p>I known that 'is' in Python is compare two object's id. But why the same compare will return different result?</p>
  
  <p>Here is a example code for my question. (Python 2 and 3 as same)</p>
  
  <pre><code>&gt;&gt;&gt; x = '123'
  &gt;&gt;&gt; y = '123'
  &gt;&gt;&gt; x is y
  True
  &gt;&gt;&gt; x *= 100
  &gt;&gt;&gt; y *= 100
  &gt;&gt;&gt; x is y
  False
  </code></pre>