title: How to use f-string formatting around a string of a dictionary
body: <p>The following code causes an Invalid Format Specifier when the string is converted to an f-string. I can't pinpoint what the problem is as my quotations look okay.</p>
  
  <pre><code>expected_document = f'{"name":"tenders","value":"chicken","key":"{key}"}'
  </code></pre>
  
  <p>causes:</p>
  
  <pre><code>&gt;       expected_document = f'{"name":"tenders","value":"chicken","key":"{key}"}'
  E       ValueError: Invalid format specifier
  </code></pre>
  
  <p>while removing the <code>f</code>:</p>
  
  <pre><code>expected_document = '{"name":"tenders","value":"chicken","key":"{key}"}'
  </code></pre>
  
  <p>works fine.</p>