def _boundary(self):
boundary = None<EOL>try:<EOL><INDENT>import uuid<EOL>boundary = uuid.uuid4().hex<EOL><DEDENT>except ImportError:<EOL><INDENT>import random, sha<EOL>bits = random.getrandbits(<NUM_LIT>)<EOL>boundary = sha.new(str(bits)).hexdigest()<EOL><DEDENT>return boundary<EOL>
Returns a random string to use as the boundary for a message.

        Returns:
            string. Boundary