How to run code on the AWS cluster using Apache-Spark?

I've written a python code on summing up all numbers in first-column for each csv file which is as follow:

import os, sys, inspect, csv

### Current directory path.
curr_dir = os.path.split(inspect.getfile(inspect.currentframe()))[0]

### Setup the environment variables
spark_home_dir = os.path.realpath(os.path.abspath(os.path.join(curr_dir, "../spark")))
python_dir = os.path.realpath(os.path.abspath(os.path.join(spark_home_dir, "./python")))
os.environ["SPARK_HOME"] = spark_home_dir
os.environ["PYTHONPATH"] = python_dir

### Setup pyspark directory path
pyspark_dir = python_dir
sys.path.append(pyspark_dir)

### Import the pyspark
from pyspark import SparkConf, SparkContext

### Specify the data file directory, and load the data files
data_path = os.path.realpath(os.path.abspath(os.path.join(curr_dir, "./test_dir")))

### myfunc is to add all numbers in the first column.
def myfunc(s):
    total = 0
    if s.endswith(".csv"):
            cr = csv.reader(open(s,"rb"))
            for row in cr:
                total += int(row[0])
                return total

def main():
### Initialize the SparkConf and SparkContext
    conf = SparkConf().setAppName("ruofan").setMaster("spark://ec2-52-26-177-197.us-west-2.compute.amazonaws.com:7077")
    sc = SparkContext(conf = conf)
    datafile = sc.wholeTextFiles(data_path)

    ### Sent the application in each of the slave node
    temp = datafile.map(lambda (path, content): myfunc(str(path).strip('file:')))

    ### Collect the result and print it out.
    for x in temp.collect():
            print x

if __name__ == "__main__":
    main()

I would like to use Apache-Spark to parallelize the summation process for several csv files using the same python code. I've already done the following steps:

1. I've created one master and two slave nodes on AWS.
2. I've used the bash command $ scp -r -i my-key-pair.pem my_dir [email protected] to upload directory my_dir including my python code with the csv files onto the cluster master node.
3. I've login my master node, and from there used the bash command $ ./spark/copy-dir my_dir to send my python code as well as csv files to all slave nodes.

4. I've setup the environment variables on the master node:

   $ export SPARK_HOME=~/spark

   $ export PYTHONPATH=$SPARK_HOME/python/:$PYTHONPATH

However, when I run the python code on the master node: $ python sum.py, it shows up the following error:

Traceback (most recent call last):
  File "sum.py", line 18, in <module>
    from pyspark import SparkConf, SparkContext
  File "/root/spark/python/pyspark/__init__.py", line 41, in <module>
    from pyspark.context import SparkContext
  File "/root/spark/python/pyspark/context.py", line 31, in <module>
    from pyspark.java_gateway import launch_gateway
  File "/root/spark/python/pyspark/java_gateway.py", line 31, in <module>
    from py4j.java_gateway import java_import, JavaGateway, GatewayClient
ImportError: No module named py4j.java_gateway

I have no ideas about this error. Also, I am wondering if the master node automatically calls all slave nodes to run in parallel. I really appreciate if anyone can help me.