input: Write a function to count the occurrence of each character in a given string. Return a dictionary where keys are the characters and values are their respective counts in the string. If the 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, 'W': 1, 'r': 1, 'd': 1, '!': 1}  
  assert char_occurrences("Python Programming")=={'P': 2, 'y': 1, 't': 1, 'h': 1, 'o': 2, 'n': 2, ' ': 1, 'r': 1, 'g': 2, 'a': 1, 'm': 2, 'i': 1}  
  assert char_occurrences("")=={}  
  assert char_occurrences("AaBbCc")=={'A': 1, 'a': 1, 'B': 1, 'b': 1, 'C': 1, 'c': 1}  
  assert char_occurrences("123456789000")=={'1': 1, '2': 1, '3': 1, '4': 1, '5': 1, '6': 1, '7': 1, '8': 1, '9': 1, '0': 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