input: Write a python function to extract words from a string.
  assert extract_words_from_string("Hello world, this is a test.") == ["Hello", "world,", "this", "is", "a", "test."]
  assert extract_words_from_string("Python is great") == ["Python", "is", "great"]
  assert extract_words_from_string("   Leading and trailing spaces   ") == ["", "", "", "Leading", "and", "trailing", "spaces", "", "", ""]
  assert extract_words_from_string("") == [""]
output: def extract_words_from_string(s):
      return s.split(' ')