input: Write a function to combine two dictionaries of similar structure together, such that the entries in the two dictionaries are merged into a single dictionary. If the given dictionaries are empty then return an empty dictionary.
  assert merge_dict({'a':1, 'b':2, 'c':3}, {'d':4, 'e':5, 'f':6})=={'a':1, 'b':2, 'c':3, 'd':4, 'e':5, 'f':6}
  assert merge_dict({}, {})=={}
  assert merge_dict({'a':1, 'b':2}, {'b':3, 'c':4})=={'a':1, 'b':3, 'c':4}
output: def merge_dict(dict1, dict2):
      result = dict1.copy()
      result.update(dict2)
      return result