docs: def _replace_by(module_function, warn=False):
      """Try replace decorated function by module.function."""
      def decorate(func, module_function=module_function, warn=warn):
          sys.path.append(os.path.dirname(__file__))
          try:
              module, function = module_function.split('.')
              func, oldfunc = getattr(__import__(module), function), func
              globals()['__old_' + func.__name__] = oldfunc
          except Exception:
              if warn:
                  warnings.warn("failed to import %s" % module_function)
          sys.path.pop()
          return func
  
      return decorate