code: def serialize_all(nodes, stream=None, Dumper=Dumper,
          canonical=None, indent=None, width=None,
          allow_unicode=None, line_break=None,
          encoding=None, explicit_start=None, explicit_end=None,
          version=None, tags=None):
      
      getvalue = None
      if stream is None:
          if encoding is None:
              stream = io.StringIO()
          else:
              stream = io.BytesIO()
          getvalue = stream.getvalue
      dumper = Dumper(stream, canonical=canonical, indent=indent, width=width,
              allow_unicode=allow_unicode, line_break=line_break,
              encoding=encoding, version=version, tags=tags,
              explicit_start=explicit_start, explicit_end=explicit_end)
      try:
          dumper.open()
          for node in nodes:
              dumper.serialize(node)
          dumper.close()
      finally:
          dumper.dispose()
      if getvalue:
          return getvalue()
docs: Serialize a sequence of representation trees into a YAML stream.
      If stream is None, return the produced string instead.