HyukjinKwon commented on a change in pull request #27406:
[SPARK-30681][PYSPARK][SQL] Add higher order functions API to PySpark
URL: https://github.com/apache/spark/pull/27406#discussion_r374068808
##########
File path: python/pyspark/sql/column.py
##########
@@ -129,6 +129,103 @@ def _(self, other):
return _
+def _unresolved_named_lambda_variable(*name_parts):
+ """
+ Create o.a.s.sql.expressions.UnresolvedNamedLambdaVariable and
+ convert it to o.s.sql.Column
+
+ :param name_parts: str
+ """
+ sc = SparkContext._active_spark_context
+ name_parts_seq = _to_seq(sc, name_parts)
+ expressions = sc._jvm.org.apache.spark.sql.catalyst.expressions
+ return Column(
+ sc._jvm.Column(
+ expressions.UnresolvedNamedLambdaVariable(name_parts_seq)
+ )
+ )
+
+
+def _get_lambda_parameters(f):
+ import inspect
+
+ signature = inspect.signature(f)
+ parameters = signature.parameters.values()
+
+ # We should exclude functions that use
+ # variable args and keyword argnames
+ # as well as keyword only args
+ supported_parmeter_types = {
+ inspect.Parameter.POSITIONAL_OR_KEYWORD,
+ inspect.Parameter.POSITIONAL_ONLY,
+ }
+
+ # Validate that
+ # function arity is between 1 and 3
+ if not (1 <= len(parameters) <= 3):
Review comment:
I actually pretty don't like such way (e.g., `_LambdaSpec(func=f,
expected_nargs={1, 2})`) which looks a bit confusing. Also, to be complete, we
should also check the input and output after `f` execution in Python side then..
The point is that, I think there might be another alternative for instance
introducing type hint into PySpark, or somehow improving error messages at
[utils.py#L76-L92](https://github.com/apache/spark/blob/0a95eb08003a115f59495b30aacaaa832940e977/python/pyspark/sql/utils.py#L76-L92)
as pointed out above. That's why I am currently thinking it might be better to
do it separately.
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