title: Return middle part of string
body: <p>I have to return the middle part of string. When the string has odd number of elements, the middle part is one letter and when the string has even number of elements, the middle part is two letters. If string is empty, return empty string</p>
  
  <pre><code>"help" -&gt; "el"
  "hi" -&gt; "hi"
  "hey" -&gt; "e"
  </code></pre>
  
  <p>I wrote a code:</p>
  
  <pre><code>if len(s) % 2 != 0:
      return s[len(s)//2]
  elif len(s) % 2 == 0:
      return s[len(s)//2 - 1] + s[len(s)//2]
  </code></pre>
  
  <p>With this I got a neede output but also an error that index is out of range. Where is mistake?</p>