docs: def get_postcodedata(self, postcode, nr, addition="", **params):
          """get_postcodedata - fetch information for 'postcode'.
  
          Parameters
          ----------
          postcode : string
              The full (dutch) postcode
  
          nr : int
              The housenumber
  
          addition : string (optional)
              the extension to a housenumber
  
          params : dict (optional)
              a list of parameters to send with the request.
  
          returns :
              a response dictionary
          """
          endpoint = 'rest/addresses/%s/%s' % (postcode, nr)
          if addition:
              endpoint += '/' + addition
  
          retValue = self._API__request(endpoint, params=params)
  
          # then it should match the houseNumberAdditions
          if addition and addition.upper() not in \
             [a.upper() for a in retValue['houseNumberAdditions']]:
              raise PostcodeError(
                      "ERRHouseNumberAdditionInvalid",
                      {"exceptionId": "ERRHouseNumberAdditionInvalid",
                       "exception": "Invalid housenumber addition: '%s'" %
                       retValue['houseNumberAddition'],
                       "validHouseNumberAdditions":
                       retValue['houseNumberAdditions']})
  
          return retValue