[SPARK-3309] [PySpark] Put all public API in __all__

Put all public API in __all__, also put them all in pyspark.__init__.py, then we can got all the documents for public API by `pydoc pyspark`. It also can be used by other programs (such as Sphinx or Epydoc) to generate only documents for public APIs.

Author: Davies Liu <davies.liu@gmail.com>

Closes #2205 from davies/public and squashes the following commits:

c6c5567 [Davies Liu] fix message
f7b35be [Davies Liu] put SchemeRDD, Row in pyspark.sql module
7e3016a [Davies Liu] add __all__ in mllib
6281b48 [Davies Liu] fix doc for SchemaRDD
6caab21 [Davies Liu] add public interfaces into pyspark.__init__.py

1 files changed, 9 insertions, 5 deletions

diff --git a/python/pyspark/__init__.py b/python/pyspark/__init__.py
index c58555fc9d..1a2e774738 100644
--- a/python/pyspark/__init__.py
+++ b/python/pyspark/__init__.py
@@ -61,13 +61,17 @@ sys.path.insert(0, s)
 
 from pyspark.conf import SparkConf
 from pyspark.context import SparkContext
-from pyspark.sql import SQLContext
 from pyspark.rdd import RDD
-from pyspark.sql import SchemaRDD
-from pyspark.sql import Row
 from pyspark.files import SparkFiles
 from pyspark.storagelevel import StorageLevel
+from pyspark.accumulators import Accumulator, AccumulatorParam
+from pyspark.broadcast import Broadcast
+from pyspark.serializers import MarshalSerializer, PickleSerializer
 
+# for back compatibility
+from pyspark.sql import SQLContext, HiveContext, SchemaRDD, Row
 
-__all__ = ["SparkConf", "SparkContext", "SQLContext", "RDD", "SchemaRDD",
-           "SparkFiles", "StorageLevel", "Row"]
+__all__ = [
+    "SparkConf", "SparkContext", "SparkFiles", "RDD", "StorageLevel", "Broadcast",
+    "Accumulator", "AccumulatorParam", "MarshalSerializer", "PickleSerializer",
+]