input: Write a function to extract the non-vowel words in a sentence. The function should take in a sentence as a string and return a list of words that do not contain any vowels.
  assert extract_words("This machine learning project is challenging.")==['This', 'machine', 'learning', 'project', 'is', 'challenging.']
  assert extract_words("Hello world!")==['world!']
  assert extract_words("Python is fun")==['Python', 'is', 'fun']
  assert extract_words("")==[]
output: def extract_words(sentence):
      vowels = "aeiouAEIOU"
      return [word for word in sentence.split() if all(char not in vowels for char in word)]