The following code tries to handle negation but gives wrong sentiment scores:

The following code tries to handle negation but gives wrong sentiment scores:

sentence = "I am not happy"
words = sentence.split()
sentiment_dict = {"happy": 1}
score = 0
negate = False
for w in words:
    if w == "not":
        negate = True
    val = sentiment_dict.get(w, 0)
    if negate:
        val = -val
    score += val
print(score)

What is the main bug causing incorrect output?