input: Write a function to count the occurrence of each character in a given string. Return the count as a dictionary where the keys are characters and the values are the number of times each character appears in the string. If the input string is empty, return an empty dictionary.
  
  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("aaabbbccc") == {'a': 3, 'b': 3, 'c': 3}
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