title: micropython f-string crash
body: <p>I am using an espressif ESP32-WROOM-32 developer board.<br>
  I have installed micropython version 18 bin on the board.<br>
  I use pycharm 2021.3.2 as IDE on a ubuntu machine.<br>
  The script sets up a WLAN connection, sets the time and tries to connect with a MQTT broker in my local network.<br>
  When I try to connect to my broker I used:</p>
  <pre><code>print(f&quot;connected to broker {config.myBroker}&quot;)
  </code></pre>
  <p>to show the status.<br>
  This repeatedly ended my script showing &quot;connect?&quot; as the last output on the REPL Terminal.<br>
  I removed the variable from the f-string and encountered the same full stop, no information at all about the crash.</p>
  <p>Once I removed the f in the statement, like:</p>
  <pre><code>print(&quot;connected to broker&quot;)
  </code></pre>
  <p>the script runs as expected.<br><br>
  Are f-strings not fully supported in micropython 18?</p>