input: Write a function to count the total number of vowels in a given string. If the given string is empty then 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")==6
  assert count_vowels("AEIOU")==5
  assert count_vowels("12345")==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