input: Write a function to find words with 4 or more characters in a given string.
  assert find_words("This is a test string with some long words") == ['This', 'test', 'string', 'with', 'some', 'long', 'words']
  assert find_words("Short words only") == []
  assert find_words("Python programming language") == ['Python', 'programming', 'language']
output: def find_words(s):
      return [word for word in s.split() if len(word) >= 4]