GNU Radio embedded python block: basic block

Hi everyone,
I want to use the embedded python block to do this:
- I have some source data bytes, and now I want to transmit a sequence of bytes before the data.
- I am thinking that the basic block is what I can use to achieve this.

However, I looked up other people's questions regarding basic blocks in the archive, i wonder if there are better examples that include forecast() and general_work() functions that I could look at?

Any suggestions will be appreciated!

Thank you

Sincerely,
Lannan Jiang