Make `true`/`false` expression JSON serializable

[Fokko]

Feature Request / Improvement

Make sure that the true/false expression can be serialized to JSON:

iceberg-python/pyiceberg/expressions/__init__.py

Lines 365 to 394 in e5e7453

	class AlwaysTrue(BooleanExpression, Singleton):
	"""TRUE expression."""
	def __invert__(self) -> AlwaysFalse:
	"""Transform the Expression into its negated version."""
	return AlwaysFalse()
	def __str__(self) -> str:
	"""Return the string representation of the AlwaysTrue class."""
	return "AlwaysTrue()"
	def __repr__(self) -> str:
	"""Return the string representation of the AlwaysTrue class."""
	return "AlwaysTrue()"
	class AlwaysFalse(BooleanExpression, Singleton):
	"""FALSE expression."""
	def __invert__(self) -> AlwaysTrue:
	"""Transform the Expression into its negated version."""
	return AlwaysTrue()
	def __str__(self) -> str:
	"""Return the string representation of the AlwaysFalse class."""
	return "AlwaysFalse()"
	def __repr__(self) -> str:
	"""Return the string representation of the AlwaysFalse class."""
	return "AlwaysFalse()"

This is a special case, since it will not translate into an object, but to a string instead:

"true"

"false"

This so-called root-model (since it doesn't convert to an object), needs to set the root:

iceberg-python/pyiceberg/transforms.py

Lines 579 to 588 in e5e7453

	class DayTransform(TimeTransform[S]):
	"""Transforms a datetime value into a day value.
	Example:
	>>> transform = DayTransform()
	>>> transform.transform(DateType())(17501)
	17501
	"""
	root: LiteralType["day"] = Field(default="day") # noqa: F821

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)

[Kaviid]

Hello,
I'm new here. I can work on this issue

[Fokko]

@Kaviid Sure thing, maybe you can pick up where others left :)