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Reject unsupported identity transform types #3517

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Reject unsupported identity transform types #3517

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Reject unsupported identity transform types
zhjwpku Jun 16, 2026
869754a
resolve review comments
zhjwpku Jun 17, 2026
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5 changes: 4 additions & 1 deletion pyiceberg/transforms.py
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Original file line number Diff line number Diff line change
Expand Up @@ -73,6 +73,8 @@
DateType,
DecimalType,
FixedType,
GeographyType,
GeometryType,
IcebergType,
IntegerType,
LongType,
Expand Down Expand Up @@ -717,7 +719,8 @@ def transform(self, source: IcebergType) -> Callable[[S | None], S | None]:
return lambda v: v

def can_transform(self, source: IcebergType) -> bool:
return source.is_primitive
# TODO: disallow VariantType when PyIceberg supports it.
return source.is_primitive and not isinstance(source, (GeographyType, GeometryType))

@rambleraptor rambleraptor Jun 16, 2026

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I completely understand that VariantType isn't a primitive, but I think we should add it here:

  • It doesn't hurt anything, since it won't be called
  • It stops a couple LLM-generated PRs come in that "notice" that VariantType is missing here
  • It makes this method explicitly match the spec. The code should match the spec. Divergences are where people begin to not trust the spec.

@zhjwpku zhjwpku Jun 16, 2026

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Yeah, I agree we should follow the spec before a decision is made to change it. However, after searching the codebase, it seems that VariantType is not currently supported in Iceberg Python, and supporting VariantType feels like a much broader effort that should probably be addressed in a separate PR, WDYT?

@rambleraptor rambleraptor Jun 17, 2026

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Maybe just add a TODO and let's move on?

@zhjwpku zhjwpku Jun 17, 2026

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Added, thanks.


def result_type(self, source: IcebergType) -> IcebergType:
return source
Expand Down
7 changes: 7 additions & 0 deletions tests/test_transforms.py
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Original file line number Diff line number Diff line change
Expand Up @@ -101,6 +101,8 @@
DoubleType,
FixedType,
FloatType,
GeographyType,
GeometryType,
IntegerType,
LongType,
NestedField,
Expand Down Expand Up @@ -255,6 +257,11 @@ def test_identity_transform_unknown_type() -> None:
assert IdentityTransform().to_human_string(UnknownType(), None) == "null"


@pytest.mark.parametrize("type_var", [GeometryType(), GeographyType()])
def test_identity_can_transform_unsupported_type(type_var: PrimitiveType) -> None:
assert not IdentityTransform().can_transform(type_var)


@ebyhr ebyhr Jun 17, 2026

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We could improve the test coverage for other methods such as transform.

If we want to test can_transform only, I suggest renaming to test_identity_can_transform_unsupported_type.

@zhjwpku zhjwpku Jun 17, 2026

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Changed as suggested, thanks

def test_string_with_surrogate_pair() -> None:
string_with_surrogate_pair = "string with a surrogate pair: 💰"
as_bytes = bytes(string_with_surrogate_pair, UTF8)
Expand Down