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Subject [GitHub] [spark] zero323 commented on a change in pull request #27406: [SPARK-30681][PYSPARK][SQL] Add higher order functions API to PySpark
Date Thu, 30 Jan 2020 20:40:22 GMT
zero323 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_r373181750
 
 

 ##########
 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:
   > What happens if I pass in a lambda that takes 3 arguments to a higher order function
like exists() that only supports 1?
   
   This is handled by the planner, which should throw an exception like this:
   
   ```
   : org.apache.spark.sql.AnalysisException: The number of lambda function arguments '2' does
not match the number of arguments expected by the higher order function '1'.;
   ```
   
   `AnalysisExceptions` are nicely captured and re-thrown by PySpark, so it seems sufficient.

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