Synonyms and Antonyms are available as part of the wordnet which a lexical database for the English language. It is available as part of nltk corpora access. In wordnet Synonyms are the words that denote the same concept and are interchangeable in many contexts so that they are grouped into unordered sets (synsets). We use these synsets to derive the synonyms and antonyms as shown in the below programs.

from nltk.corpus import wordnet

synonyms = []

for syn in wordnet.synsets("Soil"):
    for lm in syn.lemmas():
             synonyms.append(lm.name())
print (set(synonyms))

When we run the above program we get the following output −

set([grease'', filth'', dirt'', begrime'', soil'', 
grime'', land'', bemire'', dirty'', grunge'', 
stain'', territory'', colly'', ground''])

To get the antonyms we simply uses the antonym function.

from nltk.corpus import wordnet
antonyms = []

for syn in wordnet.synsets("ahead"):
    for lm in syn.lemmas():
        if lm.antonyms():
            antonyms.append(lm.antonyms()[0].name())

print(set(antonyms))

When we run the above program, we get the following output −

set([backward'', back''])