input: Write a function to count the number of vowels in a given string. The function should return the total count of vowels (both uppercase and lowercase) present in the string. If the string is empty, it should return 0.
  assert count_vowels("Hello World")==3
  assert count_vowels("Python Programming")==4
  assert count_vowels("aeiouAEIOU")==10
  assert count_vowels("")==0
  def count_vowels(string):
      count = 0
      vowels = set("aeiouAEIOU")
      for letter in string:
          if letter in vowels:
              count += 1
      return count
output: def count_vowels(string):
      count = 0
      vowels = set("aeiouAEIOU")
      for letter in string:
          if letter in vowels:
              count += 1
      return count