[SPARK-16086] [SQL] [PYSPARK] create Row without any fields

## What changes were proposed in this pull request?

This PR allows us to create a Row without any fields.

## How was this patch tested?

Added a test for empty row and udf without arguments.

Author: Davies Liu <davies@databricks.com>

Closes #13812 from davies/no_argus.

2 files changed, 12 insertions, 6 deletions

diff --git a/python/pyspark/sql/tests.py b/python/pyspark/sql/tests.py
index c631ad8a46..388ac91922 100644
--- a/python/pyspark/sql/tests.py
+++ b/python/pyspark/sql/tests.py
@@ -177,6 +177,10 @@ class DataTypeTests(unittest.TestCase):
         dt = DateType()
         self.assertEqual(dt.fromInternal(0), datetime.date(1970, 1, 1))
 
+    def test_empty_row(self):
+        row = Row()
+        self.assertEqual(len(row), 0)
+
 
 class SQLTests(ReusedPySparkTestCase):
 
@@ -318,6 +322,11 @@ class SQLTests(ReusedPySparkTestCase):
         [row] = self.spark.sql("SELECT double(add(1, 2)), add(double(2), 1)").collect()
         self.assertEqual(tuple(row), (6, 5))
 
+    def test_udf_without_arguments(self):
+        self.spark.catalog.registerFunction("foo", lambda: "bar")
+        [row] = self.spark.sql("SELECT foo()").collect()
+        self.assertEqual(row[0], "bar")
+
     def test_udf_with_array_type(self):
         d = [Row(l=list(range(3)), d={"key": list(range(5))})]
         rdd = self.sc.parallelize(d)
diff --git a/python/pyspark/sql/types.py b/python/pyspark/sql/types.py
index bb2b95404a..f0b56be8da 100644
--- a/python/pyspark/sql/types.py
+++ b/python/pyspark/sql/types.py
@@ -1401,11 +1401,7 @@ class Row(tuple):
         if args and kwargs:
             raise ValueError("Can not use both args "
                              "and kwargs to create Row")
-        if args:
-            # create row class or objects
-            return tuple.__new__(self, args)
-
-        elif kwargs:
+        if kwargs:
             # create row objects
             names = sorted(kwargs.keys())
             row = tuple.__new__(self, [kwargs[n] for n in names])
@@ -1413,7 +1409,8 @@ class Row(tuple):
             return row
 
         else:
-            raise ValueError("No args or kwargs")
+            # create row class or objects
+            return tuple.__new__(self, args)
 
     def asDict(self, recursive=False):
         """