title: What does '->' mean with function declaration in Python3?
body: <p>Recently, I have come across with '->' in Python3 when studying function declaration what does this do and mean? I have never seen such declaration other than Javascript function declaration up until now.</p>
  
  <pre><code>def f(self, s: 'str') -&gt; 'bool':
      pass
  </code></pre>