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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def attach_message(key, message):
 """Adds an attached message to the module definition. NOTE: This must be called within a `module_fn` that is defining a Module. See ModuleSpec.get_attached_message() for an introduction to attached messages and the API for module consumers. To define a new type of attached message: * Select a reasonably descriptive name as a unique key. For now, keys must be valid Python identifiers that start with a letter. Punctuation besides underscores ('_') is reserved for future use in hierarchical names. * Define a Protocol Buffer message type to store the value for the key. (Use generic containers like google.protobuf.Value only if running the protocol compiler is infeasible for your build process.) * For module consumers, consider providing a small library that encapsulates the specific call to get_attached_message() behind a higher-level interface and supplies the right message type for parsing. Attached messages work best for few messages of moderate size. Avoid a large number of messages; use repetition within messages instead. Avoid large messages (megabytes); consider module assets instead. For modules with multiple graph versions, each graph version stores separately what was attached from within the call to `module_fn` that defines its graph. Args: key: A string with the unique key to retrieve this message. Must start with a letter and contain only letters, digits and underscores. If used repeatedly within one invocation of `module_fn`, then only the message from the final call will be returned by `get_attached_message()`. message: A protocol message object, to be stored in serialized form. Raises: ValueError: if `key` is not a string of the form of a Python identifier. """

  if not re.match(r"[a-zA-Z][a-zA-Z0-9_]*$", key):
    raise ValueError(
        "hub.attach_message() called with malformed key '%s'" % key)
  saved_model_lib.attach_bytes(key, message.SerializeToString())