input: 
  def count_upper(s):
      """
      Given a string s, count the number of uppercase vowels in even indices.
      
      For example:
      count_upper('aBCdEf') returns 1
      count_upper('abcdefg') returns 0
      count_upper('dBBE') returns 0
      """
  
output:     count = 0
      vowels = "AEIOU"
      for i in range(0, len(s), 2):
          if s[i] in vowels:
              count += 1
      return count