[SPARK-29748][PYTHON][SQL] Remove Row field sorting in PySpark for version 3.6+

docs/pyspark-migration-guide.md

@@ -87,6 +87,8 @@ Please refer [Migration Guide: SQL, Datasets and DataFrame](sql-migration-guide.
   - Since Spark 3.0, `Column.getItem` is fixed such that it does not call `Column.apply`. Consequently, if `Column` is used as an argument to `getItem`, the indexing operator should be used.
     For example, `map_col.getItem(col('id'))` should be replaced with `map_col[col('id')]`.
 
+  - As of Spark 3.0 `Row` field names are no longer sorted alphabetically when constructing with named arguments for Python versions 3.6 and above, and the order of fields will match that as entered. To enable sorted fields by default, as in Spark 2.4, set the environment variable `PYSPARK_ROW_FIELD_SORTING_ENABLED` to "true". For Python versions less than 3.6, the field names will be sorted alphabetically as the only option.
+
 ## Upgrading from PySpark 2.3 to 2.4
 
   - In PySpark, when Arrow optimization is enabled, previously `toPandas` just failed when Arrow optimization is unable to be used whereas `createDataFrame` from Pandas DataFrame allowed the fallback to non-optimization. Now, both `toPandas` and `createDataFrame` from Pandas DataFrame allow the fallback by default, which can be switched off by `spark.sql.execution.arrow.fallback.enabled`.

python/pyspark/sql/tests/test_types.py

@@ -968,6 +968,19 @@ def __init__(self, **kwargs):
             with self.assertRaises(exp, msg=msg):
                 _make_type_verifier(data_type, nullable=False)(obj)
 
+    @unittest.skipIf(sys.version_info[:2] < (3, 6), "Create Row without sorting fields")
+    def test_row_without_field_sorting(self):
+        sorting_enabled_tmp = Row._row_field_sorting_enabled
+        Row._row_field_sorting_enabled = False
+
+        r = Row(b=1, a=2)
+        TestRow = Row("b", "a")
+        expected = TestRow(1, 2)
+
+        self.assertEqual(r, expected)
+        self.assertEqual(repr(r), "Row(b=1, a=2)")
+        Row._row_field_sorting_enabled = sorting_enabled_tmp
+
 
 if __name__ == "__main__":
     from pyspark.sql.tests.test_types import *

python/pyspark/sql/types.py

@@ -15,6 +15,7 @@
 # limitations under the License.
 #
 
+import os
 import sys
 import decimal
 import time
@@ -25,6 +26,7 @@
 import base64
 from array import array
 import ctypes
+import warnings
 
 if sys.version >= "3":
     long = int
@@ -1432,10 +1434,23 @@ class Row(tuple):
 
     ``key in row`` will search through row keys.
 
-    Row can be used to create a row object by using named arguments,
-    the fields will be sorted by names. It is not allowed to omit
-    a named argument to represent the value is None or missing. This should be
-    explicitly set to None in this case.
+    Row can be used to create a row object by using named arguments.
+    It is not allowed to omit a named argument to represent the value is
+    None or missing. This should be explicitly set to None in this case.
+
+    NOTE: As of Spark 3.0.0, Rows created from named arguments no longer have
+    field names sorted alphabetically and will be ordered in the position as
+    entered. To enable sorting for Rows compatible with Spark 2.x, set the
+    environment variable "PYSPARK_ROW_FIELD_SORTING_ENABLED" to "true". This
+    option is deprecated and will be removed in future versions of Spark. For
+    Python versions < 3.6, the order of named arguments is not guaranteed to
+    be the same as entered, see https://www.python.org/dev/peps/pep-0468. In
+    this case, a warning will be issued and the Row will fallback to sort the
+    field names automatically.
+
+    NOTE: Examples with Row in pydocs are run with the environment variable
+    "PYSPARK_ROW_FIELD_SORTING_ENABLED" set to "true" which results in output
+    where fields are sorted.
 
     >>> row = Row(name="Alice", age=11)
     >>> row
@@ -1474,21 +1489,40 @@ class Row(tuple):
     True
     """
 
-    def __new__(self, *args, **kwargs):
+    # Remove after Python < 3.6 dropped, see SPARK-29748
+    _row_field_sorting_enabled = \
+        os.environ.get('PYSPARK_ROW_FIELD_SORTING_ENABLED', 'false').lower() == 'true'
+
+    if _row_field_sorting_enabled:
+        warnings.warn("The environment variable 'PYSPARK_ROW_FIELD_SORTING_ENABLED' "
+                      "is deprecated and will be removed in future versions of Spark")
+
+    def __new__(cls, *args, **kwargs):
         if args and kwargs:
             raise ValueError("Can not use both args "
                              "and kwargs to create Row")
         if kwargs:
+            if not Row._row_field_sorting_enabled and sys.version_info[:2] < (3, 6):
+                warnings.warn("To use named arguments for Python version < 3.6, Row fields will be "
+                              "automatically sorted. This warning can be skipped by setting the "
+                              "environment variable 'PYSPARK_ROW_FIELD_SORTING_ENABLED' to 'true'.")
+                Row._row_field_sorting_enabled = True
+
             # create row objects
-            names = sorted(kwargs.keys())
-            row = tuple.__new__(self, [kwargs[n] for n in names])
-            row.__fields__ = names
-            row.__from_dict__ = True
-            return row
+            if Row._row_field_sorting_enabled:
+                # Remove after Python < 3.6 dropped, see SPARK-29748
+                names = sorted(kwargs.keys())
+                row = tuple.__new__(cls, [kwargs[n] for n in names])
+                row.__fields__ = names
+                row.__from_dict__ = True
+            else:
+                row = tuple.__new__(cls, list(kwargs.values()))
+                row.__fields__ = list(kwargs.keys())
 
+            return row
         else:
             # create row class or objects
-            return tuple.__new__(self, args)
+            return tuple.__new__(cls, args)
 
     def asDict(self, recursive=False):
         """

python/run-tests.py

@@ -74,7 +74,8 @@ def run_individual_python_test(target_dir, test_name, pyspark_python):
         'SPARK_TESTING': '1',
         'SPARK_PREPEND_CLASSES': '1',
         'PYSPARK_PYTHON': which(pyspark_python),
-        'PYSPARK_DRIVER_PYTHON': which(pyspark_python)
+        'PYSPARK_DRIVER_PYTHON': which(pyspark_python),
+        'PYSPARK_ROW_FIELD_SORTING_ENABLED': 'true'
     })
 
     # Create a unique temp directory under 'target/' for each run. The TMPDIR variable is