def add_doc(self, docstring):<EOL>
assert isinstance(docstring, six.text_type), type(docstring)<EOL>normalized_docstring = doc_unwrap(docstring) + '<STR_LIT:\n>'<EOL>if self.doc is None:<EOL><INDENT>self.doc = normalized_docstring<EOL><DEDENT>else:<EOL><INDENT>self.doc += normalized_docstring<EOL><DEDENT>
Adds a docstring for this namespace.

        The input docstring is normalized to have no leading whitespace and
        no trailing whitespace except for a newline at the end.

        If a docstring already exists, the new normalized docstring is appended
        to the end of the existing one with two newlines separating them.