title: Nested f-strings
body: <p>Thanks to <a href="https://twitter.com/dabeaz/status/810217326293479425?lang=en">David Beazley's tweet</a>, I've recently found out that the new <a href="https://www.python.org/dev/peps/pep-0536/">Python 3.6 f-strings</a> can also be nested:</p>
  
  <pre><code>&gt;&gt;&gt; price = 478.23
  &gt;&gt;&gt; f"{f'${price:0.2f}':*&gt;20s}"
  '*************$478.23'
  </code></pre>
  
  <p>Or:</p>
  
  <pre><code>&gt;&gt;&gt; x = 42
  &gt;&gt;&gt; f'''-{f"""*{f"+{f'.{x}.'}+"}*"""}-'''
  '-*+.42.+*-'
  </code></pre>
  
  <p>While I am surprised that this is possible, I am missing on how practical is that, when would nesting f-strings be useful? What use cases can this cover?</p>
  
  <p>Note: The PEP itself does not mention nesting f-strings, but there is a <a href="https://github.com/python/cpython/blob/master/Lib/test/test_fstring.py#L536">specific test case</a>.</p>