input: Write a function to count the total number of vowels in the given string. If the input string does not contain any vowels, it should return 0. If the input string is empty, it should also return 0.
  def count_vowels(string): 
      vowels = "aeiou"
      count = 0
      for s in string:
          if s.lower() in vowels:
              count += 1
      return count
  assert count_vowels("Hello World")==3
  assert count_vowels("Python Programming")==4
  assert count_vowels("Rhythm")==0
  assert count_vowels("")==0
output: def count_vowels(string): 
      vowels = "aeiou"
      count = 0
      for s in string:
          if s.lower() in vowels:
              count += 1
      return count