title: Single or Multiple { (curly brackets) in Python for formatting an string
body: <p>In the following ETL query we see the use of double curly brackets. </p>
  
  <pre><code>query_data = """
  SELECT {}
  FROM {}
  WHERE '{{}}'
  ORDER BY '{{}}'
  """
  </code></pre>
  
  <p>Normally, one uses a single pair of bracket with format to customize a string. So, I'm wondering which functionality carries using single or multiple curly brackets for formatting a string?. </p>