kosiew commented on code in PR #1277:
URL:
https://github.com/apache/datafusion-python/pull/1277#discussion_r2483186413
##########
python/datafusion/user_defined.py:
##########
@@ -22,15 +22,31 @@
import functools
from abc import ABCMeta, abstractmethod
from enum import Enum
-from typing import TYPE_CHECKING, Any, Callable, Optional, Protocol, TypeVar,
overload
+from typing import (
+ TYPE_CHECKING,
+ Any,
+ Callable,
+ Optional,
+ Protocol,
+ TypeVar,
+ cast,
+ overload,
+)
import pyarrow as pa
+from typing_extensions import TypeGuard
import datafusion._internal as df_internal
from datafusion.expr import Expr
if TYPE_CHECKING:
+ from _typeshed import CapsuleType as _PyCapsule
+
_R = TypeVar("_R", bound=pa.DataType)
+else:
+
+ class _PyCapsule:
+ """Lightweight typing proxy for CPython ``PyCapsule`` objects."""
Review Comment:
_typeshed.CapsuleType only exists for static type checkers, so inside the
else: branch we provide a lightweight runtime proxy to keep the _PyCapsule
symbol defined.
Without the class _PyCapsule in the else branch, the following will error:
```python
from typing import TYPE_CHECKING, TypeGuard
if TYPE_CHECKING:
from _typeshed import CapsuleType as _PyCapsule
def is_capsule(obj: object) -> TypeGuard[_PyCapsule]:
return hasattr(obj, "__capsule__")
```
```
Traceback (most recent call last):
File "/Users/kosiew/GitHub/datafusion-python/examples/example_fail.py",
line 6, in <module>
def is_capsule(obj: object) -> TypeGuard[_PyCapsule]:
^^^^^^^^^^
NameError: name '_PyCapsule' is not defined
```
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