When asked to create system XYZ and you ask to do it in Python over PHP or Ruby, what are the main features you can mention when they require you to explain it?
Give them a snippet of code in each (no more than a page) that performs some cool function that they will like. (e.g show outliers in a data set).
Show them each page. One in PHP, Ruby and Python.
Ask them which they find easiest to understand/read.
Tell them thats why you want to use Python. It's easier to read if you've not written it, more manageable, less buggy and quicker to build features because it is the most elegant (pythonic)
How to sell Python to a client/boss/person