Abacn commented on PR #40081:
URL: https://github.com/apache/beam/pull/40081#issuecomment-5626444738
Newly added test failing on Python3.10-3.12 but passing on Python3.13,3.14.
Root cause: a CPython behavior change between 3.12 and 3.13 in `issubclass()`
when dealing with `types.GenericAlias` (e.g. `tuple[int, str]`):
1. **`issubclass` difference on `GenericAlias`**:
- In **Python <= 3.12**: `issubclass(tuple[int, str], tuple)` returned
`False` directly without raising an exception.
- In **Python >= 3.13**: CPython changed `issubclass` so that passing a
`types.GenericAlias` raises `TypeError: issubclass() arg 1 must be a class`.
2. **Impact on
[_safe_issubclass](sdks/python/apache_beam/typehints/native_type_compatibility.py#L125-L138)**:
-
[_safe_issubclass](sdks/python/apache_beam/typehints/native_type_compatibility.py#L125-L138)
previously only fell back to inspecting `derived.__origin__` inside its
`except (TypeError, AttributeError):` block.
- On Python 3.13, `issubclass` raised `TypeError`, triggering the
`__origin__` check which returned `True`.
- On Python <= 3.12, `issubclass` simply returned `False`, so
`_safe_issubclass(tuple[...], tuple)` evaluated to `False`.
3. **Consequence during Schema Translation**:
- In [_safe_issubclass(type_, Sequence) and not _safe_issubclass(type_,
(str, tuple))](sdks/python/apache_beam/typehints/schemas.py#L388-L410):
- `_safe_issubclass(tuple[...], Sequence)` was `True` (because
`typing.Sequence.__subclasscheck__` raises `TypeError` across all Python
versions, triggering the fallback).
- `_safe_issubclass(tuple[...], (str, tuple))` returned `False` on
Python <= 3.12.
- As a result, Python <= 3.12 treated `tuple[...]` as an arbitrary
`Sequence` and translated it into `ArrayType` (which decodes to a `list` rather
than a `tuple`).
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