JsonSerializable.with_load() forked subclass using .from_json does not pass in forked instance.

[mjpieters]

You can create a forked JsonSerializable and attach attr_getters to this fork with a single .with_load() call, and then register deserializers. But those deserializers are ignored when using .from_json() on the subclass.

Demo:

import dataclasses, datetime, jsons

defaults = {"ham": lambda: "spam"}
forked = jsons.JsonSerializable.with_load(attr_getters=defaults, fork=True)
forked.set_deserializer(
    lambda td, cls, **kwargs: datetime.timedelta(seconds=td),
    datetime.timedelta
)

@dataclasses.dataclass
class Foo(forked):
    bar: datetime.timedelta
    ham: str

Foo.from_json({"bar": 42})

The above demo leads to a traceback:

Traceback (most recent call last):
  File ".../site-packages/jsons/_load_impl.py", line 85, in load
    return deserializer(json_obj, cls, **kwargs_)
  File ".../site-packages/jsons/deserializers/default_object.py", line 38, in default_object_deserializer
    constructor_args = _get_constructor_args(obj, cls, **kwargs)
  File ".../site-packages/jsons/deserializers/default_object.py", line 69, in _get_constructor_args
    constructor_args_in_obj = {key: value for key, value in args_gen if key}
  File ".../site-packages/jsons/deserializers/default_object.py", line 69, in <dictcomp>
    constructor_args_in_obj = {key: value for key, value in args_gen if key}
  File ".../site-packages/jsons/deserializers/default_object.py", line 68, in <genexpr>
    if sig_key != 'self')
  File ".../site-packages/jsons/deserializers/default_object.py", line 84, in _get_value_for_attr
    if obj and sig_key in obj:
TypeError: argument of type 'int' is not iterable

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File ".../site-packages/jsons/classes/json_serializable.py", line 123, in from_json
    return cls.load(json_obj, **kwargs)
  File ".../site-packages/jsons/classes/json_serializable.py", line 93, in _wrapper
    return load(inst, cls_, **{**kwargs_, **kwargs})
  File ".../site-packages/jsons/_load_impl.py", line 85, in load
    return deserializer(json_obj, cls, **kwargs_)
  File ".../site-packages/jsons/deserializers/default_object.py", line 38, in default_object_deserializer
    constructor_args = _get_constructor_args(obj, cls, **kwargs)
  File ".../site-packages/jsons/deserializers/default_object.py", line 69, in _get_constructor_args
    constructor_args_in_obj = {key: value for key, value in args_gen if key}
  File ".../site-packages/jsons/deserializers/default_object.py", line 69, in <dictcomp>
    constructor_args_in_obj = {key: value for key, value in args_gen if key}
  File ".../site-packages/jsons/deserializers/default_object.py", line 68, in <genexpr>
    if sig_key != 'self')
  File ".../site-packages/jsons/deserializers/default_object.py", line 87, in _get_value_for_attr
    meta_hints, **kwargs)
  File ".../site-packages/jsons/deserializers/default_object.py", line 122, in _get_value_from_obj
    value = load(obj[sig_key], cls_, meta_hints=new_hints, **kwargs)
  File ".../site-packages/jsons/_load_impl.py", line 89, in load
    raise DeserializationError(str(err), json_obj, cls)
jsons.exceptions.DeserializationError: argument of type 'int' is not iterable

because the replacement implementation for .load() generated by with_load() does not pass in the forked instance:

jsons/jsons/classes/json_serializable.py

Lines 91 to 95 in 03b5ff9

	@classmethod
	def _wrapper(cls_, inst, **kwargs_):
	return load(inst, cls_, **{**kwargs_, **kwargs})
	type_ = cls.fork() if fork else cls
	type_.load = _wrapper

like the original .load() implementation does:

jsons/jsons/classes/json_serializable.py

Lines 134 to 143 in 03b5ff9

	@classmethod
	def load(cls: type, json_obj: object, **kwargs) -> object:
	"""
	See ``jsons.load``.
	:param kwargs: the keyword args are passed on to the serializer
	function.
	:param json_obj: the object that is loaded into an instance of `cls`.
	:return: this instance in a JSON representation (dict).
	"""
	return load(json_obj, cls, fork_inst=cls, **kwargs)

We can work around this by creating a fork first, then using forked.with_default(..., fork_inst=forked), but is less than ideal.

[ramonhagenaars]

Hi Martijn,

Thanks for reporting this, it is a bug indeed.

[ramonhagenaars]

This bug has been resolved in v0.9.0.