dependencies for scikit learn code example

Example 1: pip install sklearn specific version

pip uninstall scikit-learn
pip install scikit-learn==0.18.2

Example 2: sklearn version

import nltk
import sklearn

print('The nltk version is {}.'.format(nltk.__version__))
print('The scikit-learn version is {}.'.format(sklearn.__version__))

# The nltk version is 3.0.0.
# The scikit-learn version is 0.15.2.