rdblue commented on code in PR #5362:
URL: https://github.com/apache/iceberg/pull/5362#discussion_r932531899
##########
python/pyiceberg/expressions/base.py:
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@@ -342,151 +313,197 @@ def __str__(self) -> str:
@dataclass(frozen=True)
-class AlwaysTrue(BooleanExpression, ABC, Singleton):
+class AlwaysTrue(BooleanExpression, Singleton):
"""TRUE expression"""
def __invert__(self) -> AlwaysFalse:
return AlwaysFalse()
@dataclass(frozen=True)
-class AlwaysFalse(BooleanExpression, ABC, Singleton):
+class AlwaysFalse(BooleanExpression, Singleton):
"""FALSE expression"""
def __invert__(self) -> AlwaysTrue:
return AlwaysTrue()
-class IsNull(UnboundPredicate[T]):
- def __invert__(self) -> NotNull:
- return NotNull(self.term)
+@dataclass(frozen=True)
Review Comment:
If we make `__invert__` abstract, then we can't use a frozen `@dataclass`
without duplicating a lot more.
The problem is, as you pointed out, `@dataclass` can't be abstract. If I
move this to the child class, `IsNull`, then the constructor no longer supports
`term` because it is defined here in the parent. Then we have to implement
`__invert__` in each child class and define the `term` separately in each child
class.
That basically removes the benefit of using a common base class. We can no
longer rely on anything higher than the leaf class having a `term` or a set of
`literals`.
I think I'd rather trade the mypy hints for `__invert__` than not be able to
rely on inheritance for expressions. That is, if I have a `UnaryPredicate`, I
want to be able to use its `term` instead of handling everything at the leaf
level.
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