title: convert list to string separated by ','in python 3.7
body: <p>I have upgraded python from 2.7 to 3.7.</p>
  
  <p>In 2.7, I do</p>
  
  <pre><code>",".join(my_list)
  </code></pre>
  
  <p>to convert from list to string, but in 3.7, I have a error:</p>
  
  <blockquote>
    <p><code>{TypeError}sequence item 0: expected str instance, bytes found</code></p>
  </blockquote>
  
  <p>How can I do this?</p>
  
  <p>I've tried adding</p>
  
  <pre><code>b','.join(mylist)
  </code></pre>
  
  <p>but it returns an error:</p>
  
  <blockquote>
    <p><code>{TypeError}sequence item 1: expected a bytes-like object, str found</code></p>
  </blockquote>
  
  <p>example:</p>
  
  <pre><code>mylist = ['try' , 'to' , 'be' , 'string']
  
  output = 'try,to,be,string'
  </code></pre>