From 0fe3bd9e9c109686b82326a50b83e16737ee1be9 Mon Sep 17 00:00:00 2001
From: Joseph Yaksich <294273268+gitcommit90@users.noreply.github.com>
Date: Mon, 29 Jun 2026 15:11:15 +0000
Subject: [PATCH 1/2] fix: reject DecimalType with precision outside [1, 38]

The Iceberg spec states precision must be 38 or less [1]. The Python
implementation silently accepted any precision, including values like
decimal(39, 0) that cannot be represented in decimal fixed-byte storage.

This aligns the Python library with the Java reference implementation
which raises IllegalArgumentException for precision > 38.

Changes:
- Add a validation check in DecimalType.__init__ that raises
  ValidationError when precision < 1 or precision > 38
- Add four tests covering: precision=39 (direct), precision=0 (direct),
  precision=38 (boundary, must pass), and precision=39 via deserialization

Fixes #3583

[1] https://iceberg.apache.org/spec/#primitive-types
---
 pyiceberg/types.py  |  2 ++
 tests/test_types.py | 26 ++++++++++++++++++++++++++
 2 files changed, 28 insertions(+)

diff --git a/pyiceberg/types.py b/pyiceberg/types.py
index 3c98215366..2449421841 100644
--- a/pyiceberg/types.py
+++ b/pyiceberg/types.py
@@ -324,6 +324,8 @@ class DecimalType(PrimitiveType):
     root: tuple[int, int]
 
     def __init__(self, precision: int, scale: int) -> None:
+        if not (1 <= precision <= 38):
+            raise ValidationError(f"Precision must be between 1 and 38 (inclusive), got: {precision}")
         super().__init__(root=(precision, scale))
 
     @model_serializer
diff --git a/tests/test_types.py b/tests/test_types.py
index 5e95687ba2..2f8a27eecc 100644
--- a/tests/test_types.py
+++ b/tests/test_types.py
@@ -521,6 +521,32 @@ def test_deserialization_decimal_failure() -> None:
     assert "Could not parse decimal(abc, def) into a DecimalType" in str(exc_info.value)
 
 
+def test_decimal_precision_above_38_raises() -> None:
+    """Precision > 38 must be rejected per the Iceberg spec (https://iceberg.apache.org/spec/#primitive-types)."""
+    with pytest.raises(ValidationError, match="Precision must be between 1 and 38"):
+        DecimalType(39, 0)
+
+
+def test_decimal_precision_zero_raises() -> None:
+    """Precision 0 is not valid; minimum precision is 1."""
+    with pytest.raises(ValidationError, match="Precision must be between 1 and 38"):
+        DecimalType(0, 0)
+
+
+def test_decimal_precision_boundary_38_accepted() -> None:
+    """Precision == 38 is the maximum allowed and must be accepted."""
+    d = DecimalType(38, 0)
+    assert d.precision == 38
+    assert d.scale == 0
+
+
+def test_decimal_deserialization_precision_above_38_raises() -> None:
+    """Deserialization of decimal(39, 0) must also raise a ValidationError."""
+    with pytest.raises(Exception, match="Precision must be between 1 and 38"):
+        DecimalType.model_validate_json('"decimal(39, 0)"')
+
+
+
 def test_str_decimal() -> None:
     assert str(DecimalType(19, 25)) == "decimal(19, 25)"
 

From 35b04394a6828f290a094d7587149c271871f390 Mon Sep 17 00:00:00 2001
From: Joseph Yaksich <294273268+gitcommit90@users.noreply.github.com>
Date: Wed, 1 Jul 2026 09:03:58 +0000
Subject: [PATCH 2/2] style: ruff format (CI lint hook)

---
 pyiceberg/table/__init__.py | 5 +++--
 tests/test_types.py         | 1 -
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/pyiceberg/table/__init__.py b/pyiceberg/table/__init__.py
index 63b87d290e..50596ff25f 100644
--- a/pyiceberg/table/__init__.py
+++ b/pyiceberg/table/__init__.py
@@ -2471,8 +2471,9 @@ def plan_files(self) -> Iterable[FileScanTask]:
             options=self.options,
         ).plan_files(
             manifests=manifests,
-            manifest_entry_filter=lambda manifest_entry: manifest_entry.snapshot_id in append_snapshot_ids
-            and manifest_entry.status == ManifestEntryStatus.ADDED,
+            manifest_entry_filter=lambda manifest_entry: (
+                manifest_entry.snapshot_id in append_snapshot_ids and manifest_entry.status == ManifestEntryStatus.ADDED
+            ),
         )
 
     def to_arrow(self) -> pa.Table:
diff --git a/tests/test_types.py b/tests/test_types.py
index 2f8a27eecc..76353f4a19 100644
--- a/tests/test_types.py
+++ b/tests/test_types.py
@@ -546,7 +546,6 @@ def test_decimal_deserialization_precision_above_38_raises() -> None:
         DecimalType.model_validate_json('"decimal(39, 0)"')
 
 
-
 def test_str_decimal() -> None:
     assert str(DecimalType(19, 25)) == "decimal(19, 25)"