code: def _resolve_filename(filename, alt=None):
      if os.path.isabs(filename):
          ...
      #        raise NotImplementedError
      else:
          filename = os.path.join(".", filename)
  
      if not alt:
          alt = filename
      elif os.path.abspath(filename) == os.path.abspath(alt):
          alt = filename
      else:
          raise ValueError(f"mismatch: {filename} != {alt}")
      return filename, alt
  
imports: import contextlib
  import os.path
label_desc: Use image node_id 4 for calling a global function with example usage: _resolve_filename(filename, alt) and returns: filename,  alt