code: def dst_to_src(self, dst_file):
          
          for map in self.mappings:
              src_uri = map.dst_to_src(dst_file)
              if (src_uri is not None):
                  return(src_uri)
          # Must have failed if loop exited
          raise MapperError(
              "Unable to translate destination path (%s) "
              "into a source URI." % (dst_file))
docs: Map destination path to source URI.