[glyph]

None of this is a problem with attrs. Serialize however you like.

    >>> import attr
    >>> 
    >>> @attr.s
    ... class Thing(object):
    ...     a = attr.ib()
    ...     b = attr.ib()
    ...     
    ... 
    >>> @attr.s
    ... class Many(object):
    ...     things = attr.ib()
    ...     
    ... 
    >>> many = Many([Thing(1, 2), Thing(3, 4)])
    >>> many
    Many(things=[Thing(a=1, b=2), Thing(a=3, b=4)])
    >>> attr.asdict(many)
    {'things': [{'a': 1, 'b': 2}, {'a': 3, 'b': 4}]}
    >>> import pickle
    >>> pickle.dumps(many)
    "ccopy_reg\n_reconstructor\np0\n(c__main__\nMany\np1\nc__builtin__\nobject\np2\n
    Ntp3\nRp4\n(dp5\nS'things'\np6\n(lp7\ng0\n(c__main__\nThing\np8\ng2\nNtp9\nRp10\
    n(dp11\nS'a'\np12\nI1\nsS'b'\np13\nI2\nsbag0\n(g8\ng2\nNtp14\nRp15\n(dp16\ng12\n
    I3\nsg13\nI4\nsbasb."
    >>> import json
    >>> json.dumps(attr.asdict(many))
    '{"things": [{"a": 1, "b": 2}, {"a": 3, "b": 4}]}'
    >>>

[rspeer]

...how does it do that?

You call attr.asdict() and it searches the attribute values, including inside lists, for more attr objects to convert into dict values?

What kinds of values does it search through? The documentation doesn't say, it just gives an example where it works inside a list for some reason.

[xapata]

Why would it need to recurse? The method probably just returns a copy of the instance's __dict__. Maybe updating it with the __slots__ and their values.

[rspeer]

It would need to recurse because you want something you can encode in JSON, not a dictionary containing a list containing miscellaneous instances.

We have an example there of an 'attrs' instance, containing a list containing 'attrs' instances, and all of the instances turn into dictionaries.