docs: def find_student_email(nb) -> str:
      '''
      Looks for the OkPy-generated string:
  
      "Successfully logged in as <email>"
  
      and returns the email address.
  
      Raises a ValueError if email not found.
      '''
      search = 'Successfully logged in as '
  
      cells = [cell for cell in nb.cells if 'outputs' in cell]
      for cell in cells:
          for output in cell.outputs:
              if 'text' in output and search in output.text:
                  return output.text.split(search)[1].strip()
      raise ValueError('Error: was not able to get email from ok.auth() cell.'
                       'Please run that cell and try again.')