code: def go_through_dict(key, d, setdefault=None):
      
      patt = re.compile(r'(?<!\\)\.')
      sub_d = d
      splitted = patt.split(key)
      n = len(splitted)
      for i, k in enumerate(splitted):
          if i < n - 1:
              if setdefault is not None:
                  sub_d = sub_d.setdefault(k, setdefault())
              else:
                  sub_d = sub_d[k]
          else:
              return k, sub_d
docs: Split up the `key` by . and get the value from the base dictionary `d`
  
      Parameters
      ----------
      key: str
          The key in the `config` configuration. %(get_value_note)s
      d: dict
          The configuration dictionary containing the key
      setdefault: callable
          If not None and an item is not existent in `d`, it is created by
          calling the given function
  
      Returns
      -------
      str
          The last level of the key
      dict
          The dictionary in `d` that contains the last level of the key