input: Write a function to count characters in a string using collections.Counter.
  assert count_characters("Python") == {'P': 1, 'y': 1, 't': 1, 'h': 1, 'o': 1, 'n': 1}
  assert count_characters("hello") == {'h': 1, 'e': 1, 'l': 2, 'o': 1}
  assert count_characters("") == {}
output: from collections import Counter
  
  def count_characters(s):
      return dict(Counter(s))