input: def count_hex_primes(hex_str):
      """Develop a function that accepts a hexadecimal string and determines 
      the count of prime digits within it. In hexadecimal, digits range from 
      0 to 9 and A to F, and prime number examples include 2, 3, 5, 7, B (which 
      corresponds to decimal 11), and D (which corresponds to decimal 13). 
      Assume the function receives valid hexadecimal strings or empty strings, 
      and letters A through F are uppercase.
      Examples:
      For hex_str = "AB" the output should be 1.
      For hex_str = "1077E" the output should be 2.
      For hex_str = "ABED1A33" the output should be 4.
      For hex_str = "123456789ABCDEF0" the output should be 6.
      For hex_str = "2020" the output should be 2.
      """
output:     
      # Set of prime digits in hexadecimal
      prime_digits = {'2', '3', '5', '7', 'B', 'D'}
      
      # Variable to count the prime digits
      count = 0
      
      # Iterate through each character in the hexadecimal string
      for char in hex_str:
          if char in prime_digits:
              count += 1
      
      return count
  