input: Write a function to combine two dictionaries into a single dictionary.
  assert combine_dicts({'a': 'apple', 'b': 'banana'}, {'c': 'cat', 'd': 'dog'}) == {'a': 'apple', 'b': 'banana', 'c': 'cat', 'd': 'dog'}
  assert combine_dicts({'x': 1, 'y': 2}, {'y': 3, 'z': 4}) == {'x': 1, 'y': 3, 'z': 4}
  assert combine_dicts({}, {'key': 'value'}) == {'key': 'value'}
  assert combine_dicts({'only_key': 'only_value'}, {}) == {'only_key': 'only_value'}
output: def combine_dicts(dict1, dict2):
      combined_dict = dict1.copy()
      combined_dict.update(dict2)
      return combined_dict