input: 
  def extract_words(sentence):
      """Extract and return a list of non-vowel words from the given sentence.
      >>> extract_words("This machine learning project is challenging.")
      ['Ths', 'mchn', 'lrnng', 'prjct', 's', 'chllngng.']
      """
      non_vowel_words = []
      words = sentence.split()
      vowels = ['a','e','i','o','u','A','E','I','O','U']
      for word in words:
          if not any(char in vowels for char in word):
              non_vowel_words.append(word) 
      return non_vowel_words
  
output:     non_vowel_words = []
      words = sentence.split()
      vowels = ['a','e','i','o','u','A','E','I','O','U']
      for word in words:
          non_vowel_word = ''.join([char for char in word if char not in vowels])
          if non_vowel_word:
              non_vowel_words.append(non_vowel_word)
      return non_vowel_words