title: import file from dag subfolder in airflow
body: <p>I am writing a python script that computes for some thing. That is why the script is separated from the dags folder. In that script, I have to import a file. But I have no success since it errors <strong>FileNotFoundError</strong>.</p>
  
  <p>This is my directory:</p>
  
  <pre><code>dags/
  - my_dag.py
    sub_folder/
    - __init__.py
    - my_functions.py
      meta/
      - file.csv
  </code></pre>
  
  <p>my_functions.py contains the computing scripts needed in my DAG. It has to read the <em>file.csv</em> located in the <em>meta</em> folder.</p>
  
  <p>In my_functions.py, I wrote:</p>
  
  <pre><code>file_df = pd.read_csv('meta/file.csv')
  </code></pre>
  
  <p>But the file cannot be found.</p>