Subsequent calls of from_dict on dataclasses that contain Optional[type] and type | None breaks behaviour because of caching

Describe the bug Exception is thrown in dacite when using from_dict in certain scenarios on dataclass with <type> | None field, eg str | None

To Reproduce

import dataclasses
import dacite
import typing

@dataclasses.dataclass
class OptionalDataclass:
    text1: typing.Optional[str]

@dataclasses.dataclass
class UnionDataclass:
    text2: str | None

if __name__ == '__main__':
    d1 = {"text1": None}
    # In order to reproduce this bug:
    # 1. this needs to be called first
    dacite.from_dict(OptionalDataclass, d1)

    # 2. this field has to be non None
    d2 = {"text2": "abc"}

    # 3. config with cast needs to be provided
    # (content of cast array does not matter, as it only is necessary to trigger
    #   for cast_type in config.cast
    # in dacite/core.py)
    c = dacite.Config(cast=[int])

    # then below fails
    res = dacite.from_dict(UnionDataclass, d2, config=c)

    # without either of 1-3 from above steps, final from_dict will work as expected

Stack trace:

/usr/local/lib/python3.10/site-packages/dacite/core.py:64: in from_dict
    value = _build_value(type_=field_type, data=field_data, config=config)
/usr/local/lib/python3.10/site-packages/dacite/core.py:101: in _build_value
    if is_subclass(type_, cast_type):
/usr/local/lib/python3.10/site-packages/dacite/types.py:174: in is_subclass
    if is_generic_collection(sub_type):
/usr/local/lib/python3.10/site-packages/dacite/types.py:147: in is_generic_collection
    origin = extract_origin_collection(type_)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

collection = str | None

    def extract_origin_collection(collection: Type) -> Type:
        try:
            return collection.__extra__
        except AttributeError:
>           return collection.__origin__
E           AttributeError: 'types.UnionType' object has no attribute '__origin__'

Root cause is caching of dacite.types.is_generic_collection and dacite.types.is_generic - caching mechanism interprets both Optional[str] and str | None as the same value, so it returns wrong value when we first call it with Optional[str], and then call it with str | None. This means first call of from_dict with OptionalDataclass pollutes the cache and breaks the behaviour for from_dict with UnionDataclass. Note that running only dacite.from_dict(UnionDataclass, d2, config=c) (without preceding call) works as expected.

To prove this, below are even simpler reproduction steps that throw exception:

if __name__ == '__main__':
    is_generic(typing.Optional[str])
    is_generic_collection(str | None)

Below works just fine:

if __name__ == '__main__':
    is_generic_collection(str | None)

thus cache pollutes scope of dacite

Removing @cache from is_generic_collection, is_generic and extract_origin_collection fixes the issue in both cases

Expected behavior Dacite transforms the data without error

Environment

Python version: 3.10
dacite version: 1.8.1

Workaround Downgrade is an option - dacite@1.7.0 works correctly

konradhalas / dacite

Subsequent calls of from_dict on dataclasses that contain Optional[type] and type | None breaks behaviour because of caching #236