TextBlob Sentiment: Calculating Polarity and Subjectivity

The TextBlob package for Python is a convenient way to do a lot of Natural Language Processing (NLP) tasks. For example:

from textblob import TextBlob
TextBlob("not a very great calculation").sentiment
## Sentiment(polarity=-0.3076923076923077, subjectivity=0.5769230769230769)

This tells us that the English phrase “not a very great calculation” has a polarity of about -0.3, meaning it is slightly negative, and a subjectivity of about 0.6, meaning it is fairly subjective.
But where do these numbers come from?

please read original post here , it is very informative
http://planspace.org/20150607-textblob_sentiment/