How to interpret this?

Question

I got the below code in a challenge but do not understand why is the answer 4. Can you help me understand please?

What is the output of this code?

Import re
sent = “hi, how, are ! you doing”
count = 0
list1 = filter(None, re.split(“[,!]+”, sent))
for i in list1:
count +=1

print(count)

Answer is 4.