input: Write a function to modify a given Python function that reads data from a JSON file to handle errors. If the file does not exist, print a message indicating that the file does not exist. If the file is not in a valid JSON format, print a message indicating that the file is not in a valid JSON format.
  
  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.")
  
  assert read_data_from_json("nonexistent_file.json")=="The file specified does not exist."
  assert read_data_from_json("invalid_json.json")=="The file specified is not in a valid JSON format."
  assert read_data_from_json("valid_json.json")=={"key": "value"}
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.")