Suppress warning about Union type about mashumaro HOT 3 OPEN

now I'm confused why this change is needed.

In short, this is closely related to the following issue:

• #42

When you define a field of type str or bool, the value is passed through as is during deserialization. So, if your Union type contains str or bool on the left, it is equivalent to having Any there instead. This is a historically accepted design decision to do this, due to the fact that, as it seemed to me, validation would not be needed, but over time I began to understand that such a clumsy method could easily lead to errors.

I added this warning just to check how many people would be affected by this change, but I didn't foresee that there would be so many of them. Now I'm going to take time out to come up with a smarter way to deserialize a Union containing str and bool. I'd like to thank all those who made me understand that it is better not to make destructive changes right now.

Right now you can remove this warning using custom deserialization methods for str and bool or for the the specific Union types:

@dataclass
class Foo(DataClassDictMixin):
    foo: str | bool | date

    class Config(BaseConfig):
        serialization_strategy = {
            bool: {"deserialize": ...},
            str: {"deserialize": ...},
        }

Another way it to keep the default implementation and suppress the warning using warnings.filterwarnings:

import warnings

warnings.filterwarnings('ignore', category=UserWarning, module='mashumaro')

I will leave this issue open for now to collect more feedback and discuss the behavior with Union. I'd love to hear about your deserialization expectations for the following examples:

@dataclass
class Foo(DataClassDictMixin):
    foo: Union[str, int]

Foo.from_dict({"foo": "1"})
Foo.from_dict({"foo": 1})

@dataclass
class Foo(DataClassDictMixin):
    foo: Union[int, str]

Foo.from_dict({"foo": "1"})
Foo.from_dict({"foo": 1})

@dataclass
class Foo(DataClassDictMixin):
    foo: Union[str, date]

Foo.from_dict({"foo": "2024-05-28"})

@dataclass
class Foo(DataClassDictMixin):
    foo: Union[date, str]

Foo.from_dict({"foo": "2024-05-28"})

@dataclass
class Foo(DataClassDictMixin):
    foo: Union[bool, int]

Foo.from_dict({"foo": 1})
Foo.from_dict({"foo": True})
Foo.from_dict({"foo": "1"})

@dataclass
class Foo(DataClassDictMixin):
    foo: Union[int, bool]

Foo.from_dict({"foo": 1})
Foo.from_dict({"foo": True})
Foo.from_dict({"foo": "1"})

from mashumaro.

We're also seeing a similar warning in dbt-core, from these two lines:

• https://github.com/dbt-labs/dbt-core/blob/main/core/dbt/contracts/graph/unparsed.py#L540
• https://github.com/dbt-labs/dbt-core/blob/main/core/dbt/contracts/graph/unparsed.py#L623

UserWarning: dbt.contracts.graph.unparsed.UnparsedMetricTypeParams.expr (typing.Union[str, bool, None]): In the next release, data marked with Union type containing 'str' and 'bool' will be coerced to the value of the type specified first instead of passing it as is

Also curious what the recommended workaround here would be

from mashumaro.

Thanks for the detailed answer and the recommended workarounds.
I understand the reasoning and at the same time I think I also can give you the answer to your question about expectations.

To me at least, I don't expect mashumaro to automatically coerce values into a type. That would be a nice to have but only if everything else failed (and even then only as option).

So, some examples;

foo: Union[int, str]
Foo.from_json({"foo": "1"}). --> "1" and not 1
Foo.from_json({"foo": 1}) --> 1 and not "1"

foo: Union[int, bool]
Foo.from_json({"foo": "1"}). --> ValueError
Foo.from_json({"foo": 1}) --> 1 and not True
Foo.from_json({"foo": "true"}) --> ValueError
Foo.from_json({"foo": true}) --> True

Maybe, just maybe, accept coercing only for Non-union types with some config parameter.

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