input: Write a function to count the number of words in a string. The function should return the count of words as an integer. If the string is empty, the function should return 0.
  assert count_words('Hello world, this is a sentence.')==5
  assert count_words('')==0
  assert count_words('This is another example.')==4
  assert count_words('SingleWord')==1
output: def count_words(s):
      if not s:
          return 0
      return len(s.split())