input: Write a function to count the occurrence of each character in a given input string. The function should return a dictionary where keys are characters and values are the number of times each character appears in the string.
  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("abracadabra") == {'a': 5, 'b': 2, 'r': 2, 'c': 1, 'd': 1}
  assert char_occurrences("123") == {'1': 1, '2': 1, '3': 1}
  assert char_occurrences("") == {}
  assert char_occurrences("x") == {'x': 1}
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