code: def update_existing(dict1, dict2, copy=False, assert_exists=False,
                      iswarning=False, alias_dict=None):
      r
      if assert_exists:
          try:
              assert_keys_are_subset(dict1, dict2)
          except AssertionError as ex:
              from utool import util_dbg
              util_dbg.printex(ex, iswarning=iswarning, N=1)
              if not iswarning:
                  raise
      if copy:
          dict1 = dict(dict1)
      if alias_dict is None:
          alias_dict = {}
      for key, val in six.iteritems(dict2):
          key = alias_dict.get(key, key)
          if key in dict1:
              dict1[key] = val
      return dict1