how to run a program in python throw the cmd in python 2 code example

Example 1: how to run python in terminal

#For Python 3:
$ python3 helloworld.py
#For Python 2:
$ python helloworld.py

Example 2: python if run in terminal

import sys
if sys.stdin.isatty():
    # running interactively
    print "running interactively"
else:
    with open('output','w') as f:
        f.write("running in the background!\n")