Lemmatization is the process of reducing a word to its base or dictionary form (lemma) by considering its context, part of speech, and using linguistic rules.
from nltk.stem import WordNetLemmatizer,PorterStemmer
stem=PorterStemmer()
lem=WordNetLemmatizer()
print(stem.stem('change'))
print(stem.stem('changes'))
print(stem.stem('changed'))
Output: chang chang chang
In stemming, it doesn’t the meaning of word or context of word, it simply changed the suffix of ‚change‘ and made word ‚chang‘ which doesn’t make any sense.
print(lem.lemmatize('change'))
print(lem.lemmatize('changes'))
print(lem.lemmatize('changed'))
Output: change change changed
Only ‚Changes‘ changed because in dictionary there no word ‚changes‘ and changed obviously it is in past tense. ‚Change‘ word is core word.