Some code to compute the corpus size.

wordcounter.py

file = open('sentences.txt', 'r', encoding="utf8")
sentences = file.read()

def tokenize():
    if sentences is not None:
        words = sentences.lower().split()
        return words
    else:
        return None

def map_book(tokens):
    hash_map = {}

    if tokens is not None:
        for element in tokens:
            # Remove Punctuation
            word = element.replace(",", "")
            word = word.replace(".", "")
            word = word.replace("?", "")
            word = word.replace(":", "")
            word = word.replace("!", "")
            word = word.replace(";", "")
            word = word.replace("\"", "")

            # Word Exist?
            if word in hash_map:
                hash_map[word] = hash_map[word] + 1
            else:
                hash_map[word] = 1

        return hash_map
    else:
        return None


# Tokenize the Book
words = tokenize()

# Create a Hash Map (Dictionary)
map = map_book(words)

print(len(map))

# Close the sentences file
file.close()