Can't I define a decorator in a separate file and import it?

[Saqib Ali]

I'm using this decorator to implement singleton class in python:

http://stackoverflow.com/posts/7346105/revisions

The strategy described above works if and only if the Singleton is
declared and defined in the same file. If it is defined in a different
file and I import that file, it doesn't work.

Why can't I import this Singleton decorator from a different file?
What's the best work around?