title: how can I convert a 'hello world' to b'hello world'
body: <p>I want to convert a string</p>
  
  <pre><code>'hello world'
  </code></pre>
  
  <p>to </p>
  
  <pre><code>b'hello world'
  </code></pre>
  
  <p>in python, how can I do that?</p>