How to pass arguments to python node

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If you aren't going to use ROS parameters, this basically a generic Python question. You should use the 'sys' module:

#!/usr/bin/env python
from __future__ import print_function
import roslib; roslib.load_manifest('my_package')
import rospy
import sys

def my_node(myArg1,myArg2)
    ...

if __name__=="__main__":
    if len(sys.argv) < 3:
        print("usage: my_node.py arg1 arg2")
    else:
        my_node(sys.argv[1], sys.argv[2])

It's also good practice (but not required) to use the <if __name__="="__main_""> stuff so that if you import this file into another one it does not run. Finally, the above example uses __future__'s print_function so that you are Python 3 compatible.