How safe is this way of getting a default that allows None?

[Tim Chase]

On 12/25/11 18:49, Dan Stromberg wrote:
> How safe is this?  I like the idea.
>
> UNSPECIFIED = object()
>
> def fn(x, y=UNSPECIFIED):
>     if y is UNSPECIFIED:
>        print x, 'default'
>     else:
>        print x, y

safe?  It's idiomatic :)

-tkc