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When parsing with Union Optional values are swallowing the input #263

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m-aciek opened this issue Oct 22, 2024 · 0 comments · May be fixed by #264
Open

When parsing with Union Optional values are swallowing the input #263

m-aciek opened this issue Oct 22, 2024 · 0 comments · May be fixed by #264
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bug Something isn't working

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@m-aciek
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m-aciek commented Oct 22, 2024 •
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Hi, thanks for your work on the library.

Describe the bug

When parsing with union an Optional value in a dataclass doesn't consider the existence of keys in dictionaries when parsing the structure. Please see the reproducer.

To Reproduce
Consider the code below:

from dataclasses import dataclass
from typing import Union, Optional

import dacite


@dataclass
class OptionalDataclass:
    optional: Optional[int]

@dataclass
class Required:
    required: int

@dataclass
class UnionDataclass:
    field: Union[OptionalDataclass, Required]


print(dacite.from_dict(UnionDataclass, {"field": {"required": 2}}))
# UnionDataclass(field=OptionalDataclass(optional=None))

Expected behavior

print(dacite.from_dict(UnionDataclass, {"field": {"required": 2}}))
# UnionDataclass(field=Required(required=2))

I would expect dacite to look into dictionary keys and prefer an object which has the key.

Environment

  • Python version: 3.9
  • dacite version: 1.8.1

Additional context

Changing the order of classes in the Union annotation helps in this case.

from dataclasses import dataclass
from typing import Union, Optional

import dacite


@dataclass
class OptionalDataclass:
    optional: Optional[int]

@dataclass
class Required:
    required: int

@dataclass
class UnionDataclass:
    field: Union[Required, OptionalDataclass]


print(dacite.from_dict(UnionDataclass, {"field": {"required": 2}}))
# UnionDataclass(field=Required(required=2))
@m-aciek m-aciek added the bug Something isn't working label Oct 22, 2024
@m-aciek m-aciek linked a pull request Oct 22, 2024 that will close this issue
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Union matches: select type by number of matching fields m-aciek/dacite
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@m-aciek