input: 
  def extract_words(sentence: str) -> List[str]:
      """Extracts all words from a sentence that do not contain any vowels (either lowercase or uppercase).
      
      >>> extract_words("This machine learning project is challenging.")
      ['machine', 'learning', 'project', 'is', 'challenging']
      """
  
output:     vowels = "aeiouAEIOU"
      words = sentence.split()
      result = [word for word in words if all(v not in word for v in vowels)]
      return result