In [1]:
# Import Dependencies
import nltk
from nltk.corpus import wordnet

In [2]:
text = 'I was not happy with the teams performance.'

In [3]:
words = nltk.word_tokenize(text)

In [4]:
words


Out[4]:
['I', 'was', 'not', 'happy', 'with', 'the', 'teams', 'performance', '.']

In [5]:
new_words = []

In [6]:
temp_word = ""
antonyms = []

In [7]:
for word in words:
    if word == 'not':
        temp_word = 'not_'
    elif temp_word == 'not_':
        for syn in wordnet.synsets(word):
            for s in syn.lemmas():
                for a in s.antonyms():
                    antonyms.append(a.name())
        if len(antonyms) >= 1:
            word = antonyms[0]
        else:
            word = temp_word + word
        temp_word = ''
    if word != 'not':
        new_words.append(word)

In [8]:
new_words


Out[8]:
['I', 'was', 'unhappy', 'with', 'the', 'teams', 'performance', '.']

In [9]:
sentence = ' '.join(new_words)

In [10]:
sentence


Out[10]:
'I was unhappy with the teams performance .'