input: Write a function to count the occurrence of each character in a given input string. Return 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.
  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}
  assert char_occurrences("Python Programming")=={'P': 2, 'y': 1, 't': 1, 'h': 1, 'o': 1, 'n': 2, ' ': 1, 'r': 2, 'g': 2, 'a': 1, 'm': 2, 'i': 1}
output: def char_occurrences(input_string):
      if not input_string:
          return {}
      char_count = {}
      for char in input_string:
          if char in char_count:
              char_count[char] += 1
          else:
              char_count[char] = 1
      return char_count