RuntimeError: dictionary changed size during iteration

[Yoriz]

I am not getting the error that you did, you didn't give a sample of word_sent so i made my own.

You should give a proper sample of word_sent so it can be tested in the same condition.

from collections import defaultdict

word_sent = [
    ["word", "word2", "word3", "word"],
    ["word5", "word1", "word1", "word"],
    ["word5", "word2", "word2", "word"],
]

freq = defaultdict(int)
for sentence in word_sent:  # word_sent is my list of lists that I mentioned above.
    for word in sentence:
        freq[word] += 1

print(freq)

Output:
defaultdict(<class 'int'>, {'word': 4, 'word2': 3, 'word3': 1, 'word5': 2, 'word1': 2})