Finding the occurrences of all words in movie scripts
A few things I can think of are:


parse_text can be marked as a private method. def _parse_text(self):. I understand this won't actually be hidden, but its a convention followed in python to treat methods starting with an underscore as private.
In MovieScript __init__ method maybe have the url as a kwarg (defaulting to http://www.springfieldspringfield.co.uk, but can be overwritten and point to another site in case you ever have to scrape another site)
In def get_text: You can cache the result from the request.get you're running and check the cache before making the request
Finally consider moving the logic of calculating the top keywords inside the MovieScript class itself (call it something like def get_common_words(self, count=20):) and allow the count to change in case you ever want more than the default.


I'm sure there are more and people will have there own preferences, but this is just what I could suggest in a quick glimpse :)