code: def calculate_delta_date(literal):
      
      mapping = {
          "today": 0,
          "yesterday": 1,
          "this-week": 7,
          "this-month": 30,
          "this-year": 365,
      }
      today = DateTime(DateTime().Date())  # current date without the time
      return today - mapping.get(literal, 0)
docs: Calculate the date in the past from the given literal
      :param literal: A date literal, e.g. "today"
      :type literal: str
      :returns: Date between the literal and today
      :rtype: DateTime