code: def maybe_stream(s):
      
      if isinstance(s, Stream):
          return s
  
      if s is None:
          stream = InMemStream()
          stream.close()  # we don't intend to write anything
          return stream
  
      if isinstance(s, unicode):
          s = s.encode('utf-8')
      if isinstance(s, bytearray):
          s = bytes(s)
  
      if isinstance(s, bytes):
          stream = InMemStream(s)
          stream.close()  # we don't intend to write anything
          return stream
  
      # s may still conform to the Stream interface. Yay duck typing.
      return s
docs: Ensure that the given argument is a stream.