sentiment analysis nltk python
What you're doing right now is a traditional classification using supervised learning. This is a great method for predicting outcomes, but I suspect there are much better ways to complete this sentiment analysis project you're working on.

Without knowing what the goal of your analysis is, I would suggest you look at the NLTK package. A lot of work has been done to idenify how positive or negative a collection of words is, and you could piggyback on the work of some really smart people. 

If you're having trouble starting, you can look at NLTK's how-to tutorial, some Kaggle kernels, or find some articles online.

Good luck!