Using NLTK to replace all words in a string with their synonyms.

plag.py

from nltk.corpus import wordnet
from nltk.tokenize import word_tokenize
from random import randint
import nltk.data

# Load a text file if required
text = "Pete ate a large cake. Sam has a big mouth."
output = ""

# Load the pretrained neural net
tokenizer = nltk.data.load('tokenizers/punkt/english.pickle')

# Tokenize the text
tokenized = tokenizer.tokenize(text)

# Get the list of words from the entire text
words = word_tokenize(text)

# Identify the parts of speech
tagged = nltk.pos_tag(words)

for i in range(0,len(words)):
    replacements = []

    # Only replace nouns with nouns, vowels with vowels etc.
    for syn in wordnet.synsets(words[i]):

        # Do not attempt to replace proper nouns or determiners
        if tagged[i][1] == 'NNP' or tagged[i][1] == 'DT':
            break
        
        # The tokenizer returns strings like NNP, VBP etc
        # but the wordnet synonyms has tags like .n.
        # So we extract the first character from NNP ie n
        # then we check if the dictionary word has a .n. or not 
        word_type = tagged[i][1][0].lower()
        if syn.name().find("."+word_type+"."):
            # extract the word only
            r = syn.name()[0:syn.name().find(".")]
            replacements.append(r)

    if len(replacements) > 0:
        # Choose a random replacement
        replacement = replacements[randint(0,len(replacements)-1)]
        output = output + " " + replacement
    else:
        # If no replacement could be found, then just use the
        # original word
        output = output + " " + words[i]

print(output)