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Fixes to dataclass transformer union handling #3248

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Fixes to dataclass transformer union handling #3248

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1a25939
fixes faulty dataclass type introspection
salotz May 13, 2025
3d543ed
fixes handling of union types
salotz May 16, 2025
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22 changes: 17 additions & 5 deletions flytekit/core/type_engine.py
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Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,7 @@
import sys
import textwrap
import threading
import types
import typing
from abc import ABC, abstractmethod
from collections import OrderedDict
Expand Down Expand Up @@ -530,10 +531,7 @@ def assert_type(self, expected_type: Type[DataClassJsonMixin], v: T):
# However, FooSchema is created by flytekit and it's not equal to the user-defined dataclass (Foo).
# Therefore, we should iterate all attributes in the dataclass and check the type of value in dataclass matches the expected_type.

expected_fields_dict = {}

for f in dataclasses.fields(expected_type):
expected_fields_dict[f.name] = f.type
expected_fields_dict = typing.get_type_hints(expected_type)

if isinstance(v, dict):
original_dict = v
Expand Down Expand Up @@ -568,7 +566,13 @@ def assert_type(self, expected_type: Type[DataClassJsonMixin], v: T):
original_type = type(v)
if UnionTransformer.is_optional_type(expected_type):
expected_type = UnionTransformer.get_sub_type_in_optional(expected_type)
if original_type != expected_type:

if UnionTransformer.is_union(expected_type) and UnionTransformer.in_union(
original_type, expected_type
):
pass

elif original_type != expected_type:
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Can we do something like this instead to make code structure better?

is_in_union = (
    UnionTransformer.is_union(expected_type)
    and UnionTransformer.in_union(original_type, expected_type)
)

if not is_in_union and original_type != expected_type:
    raise TypeTransformerFailedError(
        f"Type of Val '{original_type}' is not an instance of {expected_type}"
    )

raise TypeTransformerFailedError(
f"Type of Val '{original_type}' is not an instance of {expected_type}"
)
Expand Down Expand Up @@ -1839,6 +1843,14 @@ class UnionTransformer(AsyncTypeTransformer[T]):
def __init__(self):
super().__init__("Typed Union", typing.Union)

@staticmethod
def is_union(t: Type[Any] | types.UnionType) -> bool:
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Can we use typing.Union here? So that we do not need to import types

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If you are maintaining strict type checking, unfortunately no. As you need to check for UnionType and Union separately and UnionType doesn't fall under Type[Any] (union types are weird in Python...).

I noticed a couple other problems that were due to type mismatches so I'll defer to your preferences here as I don't want to overhaul things.

return _is_union_type(t)

@staticmethod
def in_union(t: Type[Any], union: types.UnionType) -> bool:
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Can we use typing.Union here? So that we do not need to import types

return t in typing.get_args(union)
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@machichima machichima May 24, 2025 •
edited
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Can we use get_args here instead of typing.get_args? Which is already imported


@staticmethod
def is_optional_type(t: Type) -> bool:
return _is_union_type(t) and type(None) in get_args(t)
Expand Down
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