follow pep8 None should be compared using is or is not

http://legacy.python.org/dev/peps/pep-0008/
## Programming Recommendations
- Comparisons to singletons like None should always be done with is or is not, never the equality operators.

Author: Ken Takagiwa <ken@Kens-MacBook-Pro.local>

Closes #1422 from giwa/apache_master and squashes the following commits:

7b361f3 [Ken Takagiwa] follow pep8 None should be checked using is or is not

1 files changed, 2 insertions, 2 deletions

diff --git a/python/pyspark/shell.py b/python/pyspark/shell.py
index ebd714db7a..2ce5409cd6 100644
--- a/python/pyspark/shell.py
+++ b/python/pyspark/shell.py
@@ -35,7 +35,7 @@ from pyspark.context import SparkContext
 from pyspark.storagelevel import StorageLevel
 
 # this is the equivalent of ADD_JARS
-add_files = os.environ.get("ADD_FILES").split(',') if os.environ.get("ADD_FILES") != None else None
+add_files = os.environ.get("ADD_FILES").split(',') if os.environ.get("ADD_FILES") is not None else None
 
 if os.environ.get("SPARK_EXECUTOR_URI"):
     SparkContext.setSystemProperty("spark.executor.uri", os.environ["SPARK_EXECUTOR_URI"])
@@ -55,7 +55,7 @@ print("Using Python version %s (%s, %s)" % (
     platform.python_build()[1]))
 print("SparkContext available as sc.")
 
-if add_files != None:
+if add_files is not None:
     print("Adding files: [%s]" % ", ".join(add_files))
 
 # The ./bin/pyspark script stores the old PYTHONSTARTUP value in OLD_PYTHONSTARTUP,