input: Write a function that reads data from a JSON file and handles errors. The function should return the data if the file is read successfully, or print an appropriate error message if the file does not exist or if 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("valid_file.json")=={"key": "value"}
  assert read_data_from_json("invalid_file.json")=="The file specified is not in a valid JSON format."
  assert read_data_from_json("nonexistent_file.json")=="The file specified does not exist."
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.")