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February 14, 2022 09:54
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Convert a nested structure of dict and list to dataclasses
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| import typing | |
| from dataclasses import is_dataclass | |
| def isgeneric(annot): | |
| return hasattr(annot, "__origin__") \ | |
| and hasattr(annot, "__args__") | |
| def construct(annot, json): | |
| """Construct an object from a given type from a JSON stream. | |
| The `annot` type should be one of: str, int, list[T], Optional[T], | |
| or a dataclass, and the JSON data should match exactly the given | |
| definitions in the dataclass hierarchy. | |
| """ | |
| if annot is str: | |
| assert isinstance(json, str) | |
| return json | |
| if annot is int: | |
| assert isinstance(json, int) | |
| return json | |
| if isgeneric(annot) and typing.get_origin(annot) is list: | |
| assert isinstance(json, list) | |
| return [construct(typing.get_args(annot)[0], item) for item in json] | |
| if isgeneric(annot) and typing.get_origin(annot) is Union \ | |
| and typing.get_args(annot)[1] is types.NoneType: | |
| if json is None: | |
| return None | |
| else: | |
| return construct(typing.get_args(annot)[0], json) | |
| if is_dataclass(annot): | |
| assert isinstance(json, dict) | |
| arg_annot = typing.get_type_hints(annot) | |
| assert all(k in json for k in arg_annot) | |
| args = { k: construct(v, json[k]) | |
| for k, v in arg_annot.items() } | |
| return annot(**args) |
no I misunderstood, the json is already classes
construct(list(list()), [['a']['b']])
would work
Actually:
>>> construct(list[list[str]], [['a'],['b']])
[['a'],['b']]which is a bit silly, but at least you have validated the schema. A better example:
@dataclass
class Pt:
a: int
b: int
construct(list[Pt], [{'a': 1, 'b': 2}, {'a': 3, 'b': 4}])
#> [Pt(1, 2), Pt(3, 4)]The proper way to go is to use the dacite libary, which does pretty much the same (https://github.com/konradhalas/dacite)
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Something like this?