What are all possible pos tags of NLTK?

Question

How do I find a list with all possible pos tags used by the Natural Language Toolkit (nltk)?

Answer 1

Just run this verbatim.

import nltk
nltk.download('tagsets')
nltk.help.upenn_tagset()

nltk.tag._POS_TAGGER won't work. It will give AttributeError: module 'nltk.tag' has no attribute '_POS_TAGGER'. It's not available in NLTK 3 anymore.