Python 3.8+ Nested data objects type validation with dacite

Question

I have a question regrading nested data objects.

As suggested in other post (Creating nested dataclass objects in Python), we can use dacite package to create nested data objects. This works on handling the data that we nested dictionary structure.

from dataclasses import dataclass
from dacite import from_dict

@dataclass
class A:
    x: str
    y: int

@dataclass
class B:
    a: A

data = {
    'a': {
        'x': 'test',
        'y': 1,
    }
}

result = from_dict(data_class=B, data=data)

assert result == B(a=A(x='test', y=1))

However I have a data type check function and type conversion function associate with the dataclass A in the example. Where I use inspect.signature(A).parameters to get the expected type of the dataclass and check if data are in the expected type. Can we also call the signature of class A from class B or is there any work around on this? Thanks.

The type current type check code is something like this:

expected_para = inspect.signature(A).parameters
def type_check(d_f: dict, expected_para):
    d_new = {}
    for k in expected_para.keys():
        # get expected type
        expected_type = expected_para[k].annotation
        # check if k in d_f
        if k in d_f.keys():
            # check type
            v = d_f[k]
           #type conversion here
            d_new[k] = self.typeconversion(expected_type, v)
        else:
            d_new[k] = None
    return d_new

look at post init https://docs.python.org/3/library/dataclasses.html#post-init-processing — balderman, Dec 20 '21 at 10:44
hi @balderman I am not quite sure how post init would help in this case, would you mind elabrate more? — Nathan, Dec 20 '21 at 11:11

score 1 · Answer 1 · answered Jan 25 '22 at 18:15

1

You can write a validation function using __post_init__() like this:

@dataclass
class A:
    x: str
    y: int

    def __post_init__(self) -> None:
        assert self.y > 0, 'y must be greater than zero'

answered Jan 25 '22 at 18:15

JBCP

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Python 3.8+ Nested data objects type validation with dacite

1 Answers1