Using ZMQ source blocks with a separate process

Hi,

I would like to use one of the ZMQ source blocks (such as ZMQ PULL
Message Source) to communicate with a separate Python process. I have
been able to use various Python examples to test between processes, but
when I try to use a GRC block, it fails. Are there restrictions which
prohibit data exchange outside the gnuradio realm?

Thanks for your help.
--
Barry Duggan KV4FV