input: Write a function to extract the non-vowel words from a given sentence. Return a list of words that contain no vowels.
  assert extract_words("This machine learning project is challenging")==['T', 'm', 'ch', 'nd', '']
  assert extract_words("Hello world")==['', '']
  assert extract_words("Python is a programming language")==['', 'Py', 'ng', '']
  assert extract_words("Sky is blue")==['', '']
  assert extract_words("Brrrmmm")==['Brrrmmm']
output: def extract_words(sentence):
      vowels = "aeiouAEIOU"
      words = sentence.split()
      result = []
      for word in words:
          if all(char not in vowels for char in word):
              result.append(word)
          else:
              result.append('')
      return result