input: def read_data_from_json(filename):
      """
      Reads data from a JSON file. If the file does not exist or the file content is not in a valid JSON format, appropriate error messages are printed.
      >>> read_data_from_json('nonexistent_file.json')
      The file specified does not exist.
      >>> read_data_from_json('invalid_json_file.json')
      The file specified is not in a valid JSON format.
      """
output:     try:
          with open(filename, 'r') as file:
              data = json.load(file)
              return data
      except FileNotFoundError:
          print("The file specified does not exist.")
      except json.JSONDecodeError:
          print("The file specified is not in a valid JSON format.")