input: Write a function to count the occurrence of each character in the given string. Return the count as a dictionary where the keys are the characters and the 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("") == {}
  assert char_occurrences("aaabbcc") == {'a': 3, 'b': 2, 'c': 2}
  assert char_occurrences("123321") == {'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