input: def extract_words(sentence: str) -> list:
      """ This function extracts and returns a list of non-vowel words from a given sentence.
      >>> extract_words("This machine learning project is challenging.")
      ['Ths', 'mch', 'lrnng', 'prjct', 's', 'chllngng']
      """
output:     vowels = "aeiouAEIOU"
      words = sentence.split()
      result = []
      for word in words:
          non_vowel_word = ''.join([char for char in word if char not in vowels])
          if non_vowel_word:
              result.append(non_vowel_word)
      return result