title: Accessing the 'ds' variable in airflow
body: <p>I am able to access the macros in python code like below:</p>
  
  <pre><code>partition_dt = macros.ds_add(ds, 1)
  </code></pre>
  
  <p>But i am not able to figure out how to get hold of the <code>ds</code> variable itself which seemingly can only be accessed in templates. Any pointers?</p>