title: Prevent f string from converting float into scientific notation
body: <p>I was struck by this default behavior of f-strings in python 3.7.2:</p>
  
  <pre><code>&gt;&gt; number = 0.0000001
  &gt;&gt; string = f"Number: {number}"
  &gt;&gt; print(string)
  Number: 1e-07
  </code></pre>
  
  <p>What I expected was: <code>Number: 0.0000001</code></p>
  
  <p>This is very annoying especially for creation of filenames.
  How can I disable this automatic conversion into the scientific notation? And why is it enabled in the first place?</p>
  
  <p>Basically the opposite of this <a href="https://stackoverflow.com/q/53274821/9144990">question</a>.</p>
  
  <p><strong>Edit:</strong> I would like to avoid setting a fixed length for the float via <code>{number:.8f}</code> since my numbers have different lengths and I don't want to have any trailing zeros. I want to use the f-strings to make filenames automatically, like this: </p>
  
  <pre><code>filename = f"number_{number:.10f}_other_number_{other_number:.10f}.json"
  </code></pre>
  
  <p>I am looking for a simple modifier that can disable the automatic scientific notation while keeping the original precision of the float.</p>