def is_internal_attribute(obj, attr):
    """Test if the attribute given is an internal python attribute.  For
    example this function returns `True` for the `func_code` attribute of
    python objects.  This is useful if the environment method
    :meth:`~SandboxedEnvironment.is_safe_attribute` is overridden.

    >>> from jinja2.sandbox import is_internal_attribute
    >>> is_internal_attribute(str, "mro")
    True
    >>> is_internal_attribute(str, "upper")
    False
    """
    if isinstance(obj, types.FunctionType):
        if attr in UNSAFE_FUNCTION_ATTRIBUTES:
            return True
    elif isinstance(obj, types.MethodType):
        if attr in UNSAFE_FUNCTION_ATTRIBUTES or \
           attr in UNSAFE_METHOD_ATTRIBUTES:
            return True
    elif isinstance(obj, type):
        if attr == 'mro':
            return True
    elif isinstance(obj, (types.CodeType, types.TracebackType, types.FrameType)):
        return True
    elif isinstance(obj, types.GeneratorType):
        if attr in UNSAFE_GENERATOR_ATTRIBUTES:
            return True
    elif hasattr(types, 'CoroutineType') and isinstance(obj, types.CoroutineType):
        if attr in UNSAFE_COROUTINE_ATTRIBUTES:
            return True
    elif hasattr(types, 'AsyncGeneratorType') and isinstance(obj, types.AsyncGeneratorType):
        if attri in UNSAFE_ASYNC_GENERATOR_ATTRIBUTES:
            return True
    return attr.startswith('__')
The software uses a function that accepts a format string as an argument, but the format string originates from an external source.