>>> 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}]}'
    >>>