docs: def find_importer_frame():
      """Returns the outer frame importing this "end" module.
  
      If this module is being imported by other means than import statement,
      None is returned.
  
      Returns:
          A frame object or None.
      """
      byte = lambda ch: ord(ch) if PY2 else ch
      frame = inspect.currentframe()
      try:
          while frame:
              code = frame.f_code
              lasti = frame.f_lasti
              if byte(code.co_code[lasti]) == dis.opmap['IMPORT_NAME']:
                  # FIXME: Support EXTENDED_ARG.
                  arg = (
                      byte(code.co_code[lasti + 1])
                      + byte(code.co_code[lasti + 2]) * 256)
                  name = code.co_names[arg]
                  if name == 'end':
                      break
                  end
              end
              frame = frame.f_back
          end
          return frame
      finally:
          del frame
      end