Changes to support string transform in add_field. (#1936)

Closes #1882

# Rationale for this change
Feature request: Ability to pass transform name as string in
`add_fields`

# Are these changes tested?
Yes

# Are there any user-facing changes?
Yes. Users will be able to pass transform names as string while calling
add_fields method of update_spec.

Author: guptaakashdeep

pyiceberg/table/update/spec.py

@@ -16,15 +16,7 @@
 # under the License.
 from __future__ import annotations
 
-from typing import (
-    TYPE_CHECKING,
-    Any,
-    Dict,
-    List,
-    Optional,
-    Set,
-    Tuple,
-)
+from typing import TYPE_CHECKING, Any, Dict, List, Optional, Set, Tuple, Union
 
 from pyiceberg.expressions import (
     Reference,
@@ -47,7 +39,7 @@
     UpdatesAndRequirements,
     UpdateTableMetadata,
 )
-from pyiceberg.transforms import IdentityTransform, TimeTransform, Transform, VoidTransform
+from pyiceberg.transforms import IdentityTransform, TimeTransform, Transform, VoidTransform, parse_transform
 
 if TYPE_CHECKING:
     from pyiceberg.table import Transaction
@@ -85,11 +77,13 @@ def __init__(self, transaction: Transaction, case_sensitive: bool = True) -> Non
     def add_field(
         self,
         source_column_name: str,
-        transform: Transform[Any, Any],
+        transform: Union[str, Transform[Any, Any]],
         partition_field_name: Optional[str] = None,
     ) -> UpdateSpec:
         ref = Reference(source_column_name)
         bound_ref = ref.bind(self._transaction.table_metadata.schema(), self._case_sensitive)
+        if isinstance(transform, str):
+            transform = parse_transform(transform)
         # verify transform can actually bind it
         output_type = bound_ref.field.field_type
         if not transform.can_transform(output_type):

pyiceberg/transforms.py

@@ -111,29 +111,6 @@ def _transform_literal(func: Callable[[L], L], lit: Literal[L]) -> Literal[L]:
     return literal(func(lit.value))
 
 
-def parse_transform(v: Any) -> Any:
-    if isinstance(v, str):
-        if v == IDENTITY:
-            return IdentityTransform()
-        elif v == VOID:
-            return VoidTransform()
-        elif v.startswith(BUCKET):
-            return BucketTransform(num_buckets=BUCKET_PARSER.match(v))
-        elif v.startswith(TRUNCATE):
-            return TruncateTransform(width=TRUNCATE_PARSER.match(v))
-        elif v == YEAR:
-            return YearTransform()
-        elif v == MONTH:
-            return MonthTransform()
-        elif v == DAY:
-            return DayTransform()
-        elif v == HOUR:
-            return HourTransform()
-        else:
-            return UnknownTransform(transform=v)
-    return v
-
-
 class Transform(IcebergRootModel[str], ABC, Generic[S, T]):
     """Transform base class for concrete transforms.
 
@@ -220,6 +197,29 @@ def _transform(array: "ArrayLike") -> "ArrayLike":
         return _transform
 
 
+def parse_transform(v: Any) -> Transform[Any, Any]:
+    if isinstance(v, str):
+        if v == IDENTITY:
+            return IdentityTransform()
+        elif v == VOID:
+            return VoidTransform()
+        elif v.startswith(BUCKET):
+            return BucketTransform(num_buckets=BUCKET_PARSER.match(v))
+        elif v.startswith(TRUNCATE):
+            return TruncateTransform(width=TRUNCATE_PARSER.match(v))
+        elif v == YEAR:
+            return YearTransform()
+        elif v == MONTH:
+            return MonthTransform()
+        elif v == DAY:
+            return DayTransform()
+        elif v == HOUR:
+            return HourTransform()
+        else:
+            return UnknownTransform(transform=v)
+    return v
+
+
 class BucketTransform(Transform[S, int]):
     """Base Transform class to transform a value into a bucket partition value.
 

tests/integration/test_partition_evolution.py

@@ -140,6 +140,14 @@ def test_add_hour(catalog: Catalog) -> None:
     _validate_new_partition_fields(table, 1000, 1, 1000, PartitionField(2, 1000, HourTransform(), "hour_transform"))
 
 
+@pytest.mark.integration
+@pytest.mark.parametrize("catalog", [pytest.lazy_fixture("session_catalog_hive"), pytest.lazy_fixture("session_catalog")])
+def test_add_hour_string_transform(catalog: Catalog) -> None:
+    table = _table(catalog)
+    table.update_spec().add_field("event_ts", "hour", "str_hour_transform").commit()
+    _validate_new_partition_fields(table, 1000, 1, 1000, PartitionField(2, 1000, HourTransform(), "str_hour_transform"))
+
+
 @pytest.mark.integration
 @pytest.mark.parametrize("catalog", [pytest.lazy_fixture("session_catalog_hive"), pytest.lazy_fixture("session_catalog")])
 def test_add_hour_generates_default_name(catalog: Catalog) -> None: