Make `UnaryPredicate` predicate JSON serializable

[Fokko]

Feature Request / Improvement

Make sure that the UnaryPredicate predicate can be serialized to JSON:

iceberg-python/pyiceberg/expressions/__init__.py

Lines 432 to 443 in e5e7453

	class UnaryPredicate(UnboundPredicate[Any], ABC):
	def bind(self, schema: Schema, case_sensitive: bool = True) -> BoundUnaryPredicate[Any]:
	bound_term = self.term.bind(schema, case_sensitive)
	return self.as_bound(bound_term)
	def __repr__(self) -> str:
	"""Return the string representation of the UnaryPredicate class."""
	return f"{str(self.__class__.__name__)}(term={repr(self.term)})"
	@property
	@abstractmethod
	def as_bound(self) -> Type[BoundUnaryPredicate[Any]]: ...

This predicate has four implementations: IsNull, NotNull, IsNaN, and NotNan, and translates to:

{
    "type": "is-null" // Or not-null, is-nan, not-nan
    "term": str, // The column name
}

We use Pydantic for JSON serialization, which can be enabled by deriving from the IcebergBaseModel:

iceberg-python/pyiceberg/partitioning.py

Line 124 in e5e7453

class PartitionSpec(IcebergBaseModel):

Example tests can be found here:

iceberg-python/tests/table/test_partitioning.py

Lines 116 to 132 in e5e7453

	def test_serialize_partition_spec() -> None:
	partitioned = PartitionSpec(
	PartitionField(source_id=1, field_id=1000, transform=TruncateTransform(width=19), name="str_truncate"),
	PartitionField(source_id=2, field_id=1001, transform=BucketTransform(num_buckets=25), name="int_bucket"),
	spec_id=3,
	)
	assert (
	partitioned.model_dump_json()
	== """{"spec-id":3,"fields":[{"source-id":1,"field-id":1000,"transform":"truncate[19]","name":"str_truncate"},{"source-id":2,"field-id":1001,"transform":"bucket[25]","name":"int_bucket"}]}"""
	)
	def test_deserialize_unpartition_spec() -> None:
	json_partition_spec = """{"spec-id":0,"fields":[]}"""
	spec = PartitionSpec.model_validate_json(json_partition_spec)
	assert spec == PartitionSpec(spec_id=0)

[tanmayrauth]

Hi @Fokko, can work on this issue?

[Fokko]

Fixed in #2598