code: def register_file(
      url, filename, component_type=None, known_hash=None
  ):
      """Register file for future retrieval.
  
      This function only prepares Satpy to be able to download and cache the
      provided file. It will not download the file. See
      :func:`satpy.aux_download.retrieve` for more information.
  
      Args:
          url (str): URL where remote file can be downloaded.
          filename (str): Filename used to identify and store the downloaded
              file as.
          component_type (str or None): Name of the type of Satpy component that
              will use this file. Typically "readers", "composites", "writers",
              or "enhancements" for consistency. This will be prepended to the
              filename when storing the data in the cache.
          known_hash (str): Hash used to verify the file is downloaded correctly.
              See https://www.fatiando.org/pooch/v1.3.0/beginner.html#hashes
              for more information. If not provided then the file is not checked.
  
      Returns:
          Cache key that can be used to retrieve the file later. The cache key
          consists of the ``component_type`` and provided ``filename``. This
          should be passed to :func:`satpy.aux_download_retrieve` when the
          file will be used.
  
      """
      fname = _generate_filename(filename, component_type)
      _FILE_REGISTRY[fname] = known_hash
      _FILE_URLS[fname] = url
      return fname
  
imports: import logging
  import os
  import pooch
  import satpy
label_desc: Use image node_id 1 for calling a global function with example usage: register_file(url, filename, component_type, known_hash) and returns: fname