input: Write a function to count the occurrence of each character in a given string. Return a dictionary where the keys are characters and the values are the counts of those characters.
  def char_occurrences(a_string):
   char_count = {}
   for char in a_string:
   if char in char_count:
   char_count[char] += 1
   else:
   char_count[char] = 1
   return char_count
  
  assert char_occurrences("Hello, World!") == {'H': 1, 'e': 1, 'l': 3, 'o': 2, ',': 1, ' ': 1, 'W': 1, 'r': 1, 'd': 1, '!': 1}
  assert char_occurrences("Python") == {'P': 1, 'y': 1, 't': 1, 'h': 1, 'o': 1, 'n': 1}
  assert char_occurrences("Hello") == {'H': 1, 'e': 1, 'l': 2, 'o': 1}
  assert char_occurrences("") == {}
  assert char_occurrences("aabbcc") == {'a': 2, 'b': 2, 'c': 2}
output: def char_occurrences(a_string):
      char_count = {}
      for char in a_string:
          if char in char_count:
              char_count[char] += 1
          else:
              char_count[char] = 1
      return char_count