how to create a py file in SC code example

Example 1: how to run python in terminal

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

Example 2: to run python script in terminal i want to type python insted of python3

$ python --version
Python 2.7.6
$ python3 --version
Python 3.4.3
$ alias python=python3
$ python --version
Python 3.4.3