input: Write a function to count the total number of vowels in a given string. Vowels are defined as 'a', 'e', 'i', 'o', 'u' and both uppercase and lowercase should be considered. If the string is empty, the function should return 0.
  def count_vowels(string): 
      vowels = "aeiouAEIOU"
      count = 0
      for s in string:
          if s in vowels:
              count += 1
      return count
  assert count_vowels("Hello World")==3
  assert count_vowels("Python Programming")==4
  assert count_vowels("AEIOU")==5
  assert count_vowels("12345")==0
  assert count_vowels("")==0
output: def count_vowels(string): 
      vowels = "aeiouAEIOU"
      count = 0
      for s in string:
          if s in vowels:
              count += 1
      return count