Attribute access doesn't seem to work with old-style formatting, so I would think it's safe. >>> class foo: ... def __init__(self, **kwargs): .

Attribute access doesn't seem to work with old-style formatting, so I would think it's safe. >>> class foo: ... def __init__(self, **kwargs): ... self.__dict__.update(kwargs) ... >>> my_foo = foo(secret="bazinga") >>> >>> "%(foo)s" % {'foo': my_foo} '<__main__.foo instance at 0x1101d23f8>' >>> >>> "%(foo.secret)s" % {'foo': my_foo} Traceback (most recent call last): File "<stdin>", line 1, in <module> KeyError: 'foo.secret'