The world’s largest living snake specie in terms of weight is the green anaconda. The scientific name is Eunectes murinus. It can weigh over 200 pounds and reach lengths of 16 feet. Although some pythons can be longer, the anaconda is larger in the sense that they are heavier.
The fictional action thriller movie “Anaconda” is about that snake. However in the movie, they use a mechanical snake, which was built to a size larger than the real size one. I don’t think you can train a snake to do those things.