import nltk
word_data = "The Sky is blue also the ocean is blue also Rainbow has a blue colour." 

# First Word tokenization
nltk_tokens = nltk.word_tokenize(word_data)

# Applying Set
no_order = list(set(nltk_tokens))

print no_order

['blue', 'Rainbow', 'is', 'Sky', 'colour', 'ocean', 'also', 'a', '.', 'The', 'has', 'the']

import nltk
word_data = "The Sky is blue also the ocean is blue also Rainbow has a blue colour." 
# First Word tokenization
nltk_tokens = nltk.word_tokenize(word_data)

ordered_tokens = set()
result = []
for word in nltk_tokens:
    if word not in ordered_tokens:
        ordered_tokens.add(word)
        result.append(word)

print result

['The', 'Sky', 'is', 'blue', 'also', 'the', 'ocean', 'Rainbow', 'has', 'a', 'colour', '.']