code: def set(self, key=None, username=None, base_url=None):
          
          self.__init__(key=(key or self._key),
                        username=(username or self._username),
                        base_url=base_url)
docs: Update the credentials of a Credentials instance instead with new
          values.
  
          Args:
              key (str): API key of user account. Defaults to previous value if
                  not specified.
              username (str): User name of account. This parameter is optional if
                  `base_url` is not specified, but defaults to the previous
                  value if not set.
              base_url (str): Base URL of user account. This parameter is
                  optional if `username` is specified and on CARTO's
                  cloud-based account. Generally of the form
                  ``https://your_user_name.carto.com/`` for cloud-based accounts.
                  If on-prem or otherwise, contact your admin.
  
          Example:
  
              .. code::
  
                  from cartoframes import Credentials
                  # load credentials saved in previous session
                  creds = Credentials()
                  # set new API key
                  creds.set(key='new_api_key')
                  # save new creds to default user config directory
                  creds.save()
  
          Note:
              If the `username` is specified but the `base_url` is not, the
              `base_url` will be updated to ``https://<username>.carto.com/``.