Python coding help: Has anybody seen this syntax

[Andreas Tille <andreas@an3as.eu>]

Hi,

I'm trying to package spades[1] and found the following code inside an
__init__.py file:


...

class YAMLObjectMetaclass(type):
    """
    The metaclass for YAMLObject.
    """
    def __init__(cls, name, bases, kwds):
        super(YAMLObjectMetaclass, cls).__init__(name, bases, kwds)
        if 'yaml_tag' in kwds and kwds['yaml_tag'] is not None:
            cls.yaml_loader.add_constructor(cls.yaml_tag, cls.from_yaml)
            cls.yaml_dumper.add_representer(cls, cls.to_yaml)

class YAMLObject(metaclass=YAMLObjectMetaclass):
    """
    An object that can dump itself to a YAML stream
    and load itself from a YAML stream.
    """

    __slots__ = ()  # no direct instantiation, so allow immutable subclasses

    yaml_loader = Loader
    yaml_dumper = Dumper


...


which ends up in


  File "/usr/share/spades/pyyaml3/__init__.py", line 284
    class YAMLObject(metaclass=YAMLObjectMetaclass):
                              ^
SyntaxError: invalid syntax



I'm not a very skilled Python coder but IMHO the critical line should be
replaced by


class YAMLObject(YAMLObjectMetaclass):                                                                                                                                                                  



Is this correct?  Do you have any clue whether this is some old syntax
or what sensible hint I might give to upstream?


Thanks for your patience

      Andreas.



[1] svn://anonscm.debian.org/debian-med/trunk/packages/spades/trunk/

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