input: Write a function to modify the given Python code to handle errors. The function should open and read data from a JSON file. If the file does not exist, it should print a message indicating that the file specified does not exist. If the file is not in a valid JSON format, it should print a message indicating that the file specified is not in a valid JSON format.
  
  ### Python Code:
  def read_data_from_json(filename):
      try:
          with open(filename, 'r') as f:
              data = json.load(f)
          return data
      except FileNotFoundError:
          print("The file specified does not exist.")
      except json.decoder.JSONDecodeError:
          print("The file specified is not in a valid JSON format.")
  
  ### Test Cases:
  assert read_data_from_json("existing_file.json")=={"key": "value"}
  assert read_data_from_json("non_existing_file.json")=="The file specified does not exist."
  assert read_data_from_json("invalid_json_file.json")=="The file specified is not in a valid JSON format."
output: def read_data_from_json(filename):
      try:
          with open(filename, 'r') as f:
              data = json.load(f)
          return data
      except FileNotFoundError:
          print("The file specified does not exist.")
      except json.decoder.JSONDecodeError:
          print("The file specified is not in a valid JSON format.")