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Reject DecimalType with precision larger than 38 #3593

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Reject DecimalType with precision larger than 38 #3593

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662c0df
Reject DecimalType with precision larger than 38
kratos0718 Jul 1, 2026
f32c45d
test: use a valid precision (38) in TEST_PRIMITIVE_TYPES
kratos0718 Jul 1, 2026
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2 changes: 2 additions & 0 deletions pyiceberg/types.py
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Original file line number Diff line number Diff line change
Expand Up @@ -324,6 +324,8 @@ class DecimalType(PrimitiveType):
root: tuple[int, int]

def __init__(self, precision: int, scale: int) -> None:
if precision > 38:
raise ValueError(f"Decimals with precision larger than 38 are not supported: {precision}")
super().__init__(root=(precision, scale))

@model_serializer
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2 changes: 1 addition & 1 deletion tests/test_schema.py
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Expand Up @@ -67,7 +67,7 @@
FloatType(),
DoubleType(),
DecimalType(10, 2),
DecimalType(100, 2),
DecimalType(38, 2),
StringType(),
DateType(),
TimeType(),
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9 changes: 9 additions & 0 deletions tests/test_types.py
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Expand Up @@ -147,6 +147,15 @@ def test_decimal_type() -> None:
assert type_var == pickle.loads(pickle.dumps(type_var))


def test_decimal_type_rejects_precision_over_38() -> None:
# The Iceberg spec requires decimal precision to be 38 or less; the Java
# reference implementation raises for precision > 38. See issue #3583.
with pytest.raises(ValueError, match="precision larger than 38 are not supported: 39"):
DecimalType(39, 0)
# Boundary: precision exactly 38 is still valid.
assert DecimalType(38, 0).precision == 38


def test_struct_type() -> None:
type_var = StructType(
NestedField(1, "optional_field", IntegerType(), required=True),
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