code: def _boundary(self):
          
          boundary = None
          try:
              import uuid
              boundary = uuid.uuid4().hex
          except ImportError:
              import random, sha
              bits = random.getrandbits(160)
              boundary = sha.new(str(bits)).hexdigest()
          return boundary
docs: Returns a random string to use as the boundary for a message.
          
          Returns:
              string. Boundary