input: Write a function to count the total number of vowels in a given string. Define the function as count_vowels that takes a string as an input and returns the total number of vowels, considering both uppercase and lowercase vowels.
  
  assert count_vowels("Hello, World!")==3
  assert count_vowels("Python Programming")==4
  assert count_vowels("aeiou")==5
  assert count_vowels("ABCDEFGhijk")==3
  assert count_vowels("")==0
output: def count_vowels(s):
      vowels = "aeiouAEIOU"
      count = 0
      for char in s:
          if char in vowels:
              count += 1
      return count