The PYTHONSTARTUP variable

You can set an environment variable called PYTHONSTARTUP for Python’s console. Whenever you enter the Python console, this file will be executed, allowing for you to add extra functionality to the console such as importing commonly-used modules automatically.

If the PYTHONSTARTUP variable was set to the location of a file containing this:

print("Welcome!")

Then opening the Python console would result in this extra output:

$ py
Python 3.4.3 (v3.4.3:9b73f1c3e601, Feb 24 2015, 22:44:40) [MSC v.1600 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
Welcome!
>>>