input: Write a function to count the occurrence of each character in a given input string. Return the results as a dictionary where the keys are characters and the values are their corresponding 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("mississippi") == {'m': 1, 'i': 4, 's': 4, 'p': 2}
  assert char_occurrences("") == {}
  assert char_occurrences("a") == {'a': 1}
  assert char_occurrences("aaa") == {'a': 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