eclipse-aascw / aas-core-codegen / 35243962401

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Compose the Python JSON de-serialization (#706)

Five sixths of the generated ``jsonization.py`` was de-serialization,
and a class cost four constructs there: a ``_SetterFor<Cls>`` class, a
field on it per property, a twelve-line ``set_<prop>_from_jsonable``
method whose body was a single assignment, and a
``_SETTER_MAP_FOR_<CLS>`` of bound methods. Every
``<cls>_from_jsonable`` then re-emitted the same framing around the
property loop, and every dispatching function was the same twenty lines
with two tokens substituted in. The property loop now assigns straight
into the locals which the constructor is called with, the way the C#, Go
and Java generators already do:

    def blob_from_jsonable(jsonable):
        mapping = _as_mapping(jsonable)

        model_type = mapping.get('modelType', None)
        if model_type != 'Blob':
            raise DeserializationException(
                f"Expected modelType to be 'Blob', "
                f"but got: {model_type!r}"
            )

        the_value: Optional[bytes] = None
        the_content_type: Optional[str] = None
        ...

        try:
            for key, jsonable_value in mapping.items():
                if key == 'modelType':
                    # The model type has already been checked above.
                    pass
                elif key == 'value':
                    the_value = _bytes_from_jsonable(jsonable_value)
                ...
                else:
                    raise DeserializationException(
                        f"Unexpected property: {key}"
                    )
        except DeserializationException as exception:
            exception.path._prepend(PropertySegment(mapping, key))
            raise

The rationale and the design:

* The loop is generated per class because a shared one cannot write its
  caller's locals. That is the only reason ``_SetterFor<Cls>`` existed,
  and it cost an object allocated for every instance, a field
  initialised for every property, ... (continued)

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