title: When does a airflow dag definition get evaluated?
body: <p>Suppose I have an airflow dag file that creates a graph like so...</p>
  
  <pre class="lang-py prettyprint-override"><code>def get_current_info(filename)
      current_info = {}
      &lt;fill in info in current_info relevant for today's date for given file&gt;
      return current_info
  
  files = [
      get_current_info("file_001"),
      get_current_info("file_002"),
      ....
  ]
  
  for f in files:
      &lt;some BashOperator bo1 using f's current info dict&gt;
      &lt;some BashOperator bo2 using f's current info dict&gt;
      ....
  
      bo1 &gt;&gt; bo2
      ....
  </code></pre>
  
  <p>Since these values in the current_info dict that is used to define the dag changes periodically (here, daily), I would like to know by what process / schedule the dag definition gets updated. (I print the current_info values each run and values appear to be updating, but curious as to how and when exactly this happens).</p>
  
  <p>When does a airflow dag definition get evaluated? referenced anywhere in the docs?</p>