code: def copy_file(self, src_path, file_name, key=None):
          
          path = os.path.join(self._directories[key], file_name)
          shutil.copyfile(src_path, path)
docs: Copies a file unmodified to a location inside the ouput directory.
  
          Parameters
          ----------
          src_path: str
              Path to the src file
          file_name: str
              name of the destination file