input: Write a function to count the occurrences of each character in a given string. Return a dictionary where the keys are characters and the values are their respective counts.
  
  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("") == {}
  assert char_occurrences("abc") == {'a': 1, 'b': 1, 'c': 1}
  assert char_occurrences("123123") == {'1': 2, '2': 2, '3': 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