import attrs, cattrs
from cattrs.gen import make_dict_unstructure_fn, override

# Let's say we have a class Person which, as an implementation detail, stores its children in a dict, 
# so we can retrieve them by name.

@attrs.define
class Person:
    name: str = attrs.field()
    _children_by_name: dict[str, "Person"] = attrs.field(factory=dict)

    def add_child(self, child: "Person"):
        self._children_by_name[child.name] = child


attrs.resolve_types(Person)

alice = Person(name="Alice")
alice.add_child(Person(name="Bob"))


# Let's make our external representation a little more presentable by renaming _children_by_name to children.
c = cattrs.Converter()
c.register_unstructure_hook(Person, make_dict_unstructure_fn(Person, c, 
    _children_by_name=override(rename="children")))
# Note that just because we use an `override` with a `rename` we don't lose recursive unstructuring.
assert repr(c.unstructure(alice)) == "{'name': 'Alice', 'children': {'Bob': {'name': 'Bob', 'children': {}}}}"


# Let's use a list instead of a dict, since the name is redundant. A case for an attribute unstruct hook?
c = cattrs.Converter()
c.register_unstructure_hook(Person, make_dict_unstructure_fn(Person, c, 
    _children_by_name=override(rename="children", unstruct_hook=lambda x: list(x.values()))))
# Oh, but this is unexpected. Now Bob is not unstructured anymore.
assert repr(c.unstructure(alice)) == "{'name': 'Alice', 'children': [Person(name='Bob', _children_by_name={})]}"


# This works: calling back into the converter explicitly. But it seems surprising.
c = cattrs.Converter()
c.register_unstructure_hook(Person, make_dict_unstructure_fn(Person, c, 
    _children_by_name=override(rename="children", unstruct_hook=lambda x: c.unstructure(list(x.values())))))
assert repr(c.unstructure(alice)) == "{'name': 'Alice', 'children': [{'name': 'Bob', 'children': []}]}"