title: Why does every string contain the empty string?
body: <p>"ABCDE" has no empty character. But when I type</p>
  
  <pre><code>"" in "ABCDE"
  </code></pre>
  
  <p>Python interpreter returns <code>True</code>.</p>
  
  <p>Why?</p>
  
  <p>is there any empty character in "ABCDE"? I don't think so.</p>
  
  <p>And I also found when I use these code:</p>
  
  <pre><code>target = ''
  src = 'ABCDE'
  src.find(target)
  </code></pre>
  
  <p>it returns 0 instead of -1</p>
  
  <p>Why is this?</p>