code: def format(self, format):
      format = format.lower()
      if format not in backend.FORMATS:
          raise ValueError(f"unknown format: {format!r}")
      self._format = format
  
imports: import codecs
  import locale
  import logging
  import os
  from .None import backend
  from .None import tools
label_desc: Use image node_id 4 for calling the Base obj's underlying member method code with example usage: obj.format(format) without return types