Take CSV files of movies and TV shows and use them to update your data on Trakt.tv.
I wanted to move from a well-known internet database of movies to Trakt.tv, but I had years of extensive data on the former site. Luckily that site provides a CSV export for your data (which occasionally works =). I looked at TraktRater, but I'm an OS X user and had issues getting the C# app to work. Being a programmer I decided to solve the problem by writing my own CLI app that was as cross-platform as Python.
Because I wrote this for my own benefit and have successfully used it once to move my data over to Trakt.tv, I am not actively developing this code anymore. I am providing it to the public as-is in case someone else finds it useful.
Make sure you have Python 3.4 or newer installed.
Get a PIN
While logged into Trakt.tv, request a PIN for csv2trakt.
The PIN is good for a single use as csv2trakt doesn't bother to save to save the access token that Trakt.tv gives the app (the assumption is you will only do this once and thus it isn't necessary to support storing the access token).
Run the app
You can then look at the help of the app to see how to use it:
python3 -m csv2trakt --help