[SPARK-8698] partitionBy in Python DataFrame reader/writer interface should...

[SPARK-8698] partitionBy in Python DataFrame reader/writer interface should not default to empty tuple.

Author: Reynold Xin <rxin@databricks.com>

Closes #7079 from rxin/SPARK-8698 and squashes the following commits:

8513e1c [Reynold Xin] [SPARK-8698] partitionBy in Python DataFrame reader/writer interface should not default to empty tuple.

python/pyspark/sql/readwriter.py

@@ -270,12 +270,11 @@ class DataFrameWriter(object):
         """
         if len(cols) == 1 and isinstance(cols[0], (list, tuple)):
             cols = cols[0]
-        if len(cols) > 0:
-            self._jwrite = self._jwrite.partitionBy(_to_seq(self._sqlContext._sc, cols))
+        self._jwrite = self._jwrite.partitionBy(_to_seq(self._sqlContext._sc, cols))
         return self
 
     @since(1.4)
-    def save(self, path=None, format=None, mode=None, partitionBy=(), **options):
+    def save(self, path=None, format=None, mode=None, partitionBy=None, **options):
         """Saves the contents of the :class:`DataFrame` to a data source.
 
         The data source is specified by the ``format`` and a set of ``options``.
@@ -295,7 +294,9 @@ class DataFrameWriter(object):
 
         >>> df.write.mode('append').parquet(os.path.join(tempfile.mkdtemp(), 'data'))
         """
-        self.partitionBy(partitionBy).mode(mode).options(**options)
+        self.mode(mode).options(**options)
+        if partitionBy is not None:
+            self.partitionBy(partitionBy)
         if format is not None:
             self.format(format)
         if path is None:
@@ -315,7 +316,7 @@ class DataFrameWriter(object):
         self._jwrite.mode("overwrite" if overwrite else "append").insertInto(tableName)
 
     @since(1.4)
-    def saveAsTable(self, name, format=None, mode=None, partitionBy=(), **options):
+    def saveAsTable(self, name, format=None, mode=None, partitionBy=None, **options):
         """Saves the content of the :class:`DataFrame` as the specified table.
 
         In the case the table already exists, behavior of this function depends on the
@@ -334,7 +335,9 @@ class DataFrameWriter(object):
         :param partitionBy: names of partitioning columns
         :param options: all other string options
         """
-        self.partitionBy(partitionBy).mode(mode).options(**options)
+        self.mode(mode).options(**options)
+        if partitionBy is not None:
+            self.partitionBy(partitionBy)
         if format is not None:
             self.format(format)
         self._jwrite.saveAsTable(name)
@@ -356,7 +359,7 @@ class DataFrameWriter(object):
         self.mode(mode)._jwrite.json(path)
 
     @since(1.4)
-    def parquet(self, path, mode=None, partitionBy=()):
+    def parquet(self, path, mode=None, partitionBy=None):
         """Saves the content of the :class:`DataFrame` in Parquet format at the specified path.
 
         :param path: the path in any Hadoop supported file system
@@ -370,7 +373,9 @@ class DataFrameWriter(object):
 
         >>> df.write.parquet(os.path.join(tempfile.mkdtemp(), 'data'))
         """
-        self.partitionBy(partitionBy).mode(mode)
+        self.mode(mode)
+        if partitionBy is not None:
+            self.partitionBy(partitionBy)
         self._jwrite.parquet(path)
 
     @since(1.4)