New submission from Thomas Fischbacher <tf...@google.com>:
This problem may also be the issue underlying some other dataclasses.asdict() bugs: https://bugs.python.org/issue?%40columns=id%2Cactivity%2Ctitle%2Ccreator%2Cassignee%2Cstatus%2Ctype&%40sort=-activity&%40filter=status&%40action=searchid&ignore=file%3Acontent&%40search_text=dataclasses.asdict&submit=search&status=-1%2C1%2C2%2C3 The documentation of dataclasses.asdict() states: https://docs.python.org/3/library/dataclasses.html#dataclasses.asdict === Converts the dataclass instance to a dict (by using the factory function dict_factory). Each dataclass is converted to a dict of its fields, as name: value pairs. dataclasses, dicts, lists, and tuples are recursed into. For example: (...) === Given this documentation, the expectation about behavior is roughly: def _dataclasses_asdict_equivalent_helper(obj, dict_factory=dict): rec = lambda x: ( _dataclasses_asdict_equivalent_helper(x, dict_factory=dict_factory)) if isinstance(obj, (list, tuple)): return type(obj)(rec(x) for x in obj) elif isinstance(obj, dict): return type(obj)((k, rec(v) for k, v in obj.items()) # Otherwise, we are looking at a dataclass-instance. for field in type(obj).__dataclass_fields__: val = obj.__getattribute__[field] if (hasattr(type(obj), '__dataclass_fields__')): # ^ approx check for "is this a dataclass instance"? # Not 100% correct. For illustration only. ret[field] = rec(val) ret[field] = val return ret def dataclasses_asdict_equivalent(x, dict_factory=dict): if not hasattr(type(x), '__dataclass_fields__'): raise ValueError(f'Not a dataclass: {x!r}') return _dataclasses_asdict_equivalent(x, dict_factory=dict_factory) In particular, field-values that are neither dict, list, tuple, or dataclass-instances are expected to be used identically. What actually happens however is that .asdict() DOES call __deepcopy__ on field values it has no business inspecting: === import dataclasses @dataclasses.dataclass class Demo: field_a: object class Obj: def __init__(self, x): self._x = x def __deepcopy__(self, *args): raise ValueError('BOOM!') ### d1 = Demo(field_a=Obj([1,2,3])) dd = dataclasses.asdict(d1) # ...Execution does run into a "BOOM!" ValueError. === Apart from this: It would be very useful if dataclasses.asdict() came with a recurse={boolish} parameter with which one can turn off recursive translation of value-objects. ---------- components: Library (Lib) messages: 401360 nosy: tfish2 priority: normal severity: normal status: open title: dataclasses.asdict() incorrectly calls __deepcopy__() on values. type: behavior _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue45135> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
