code: def choose_tool_key(full_configuration, keys):
      
      tool_key = _choose_key(full_configuration.config, keys)
      if tool_key != keys[0]:
          full_configuration.executor.warning(
              "{} is deprecated; migrate to {}".format(tool_key, keys[0])
          )
      return tool_key
docs: Select the key for a tool from a list of supported tools.
  
      This function is designed to help when multiple keys can be used to specify
      an option (e.g., during migration from one name to another).  The values in
      keys should be ordered based on preference, as that's the order they'll be
      checked.  If anything other than the first entry is selected, a warning
      will be displayed telling the user to migrate their configuration.
  
      Arguments:
      full_configuration - the full configuration for a run of the project
      keys - a list of keys to consider