title: SyntaxError on "self.async" when running python kafka producer
body: <pre><code>Traceback (most recent call last):
    File &quot;//producer.py&quot;, line 1, in &lt;module&gt;
      from kafka.producer import KafkaProducer
    File &quot;/usr/local/lib/python3.9/site-packages/kafka/__init__.py&quot;, line 23, in &lt;module&gt;
      from kafka.producer import KafkaProducer
    File &quot;/usr/local/lib/python3.9/site-packages/kafka/producer/__init__.py&quot;, line 4, in &lt;module&gt;
      from .simple import SimpleProducer
    File &quot;/usr/local/lib/python3.9/site-packages/kafka/producer/simple.py&quot;, line 54
      return '&lt;SimpleProducer batch=%s&gt;' % self.async
                                                ^
  SyntaxError: invalid syntax
  
  </code></pre>
  <p>I had seen an earlier error identical but I was using <code>from kafka import KafkaProducer</code></p>
  <p>My new python script uses <code>from kafka.producer import KafkaProducer</code>but I still get the self.async error</p>