How to make a message source and message strobe blocks in GNURadio

I have to make a message source block in GNURadio. I have to use Windows 10 and I don’t know how to install and use gr-modtool on it, so I’m trying to make the block using the Embedded Python Block.

The message block shall behave in a manner similar to the Message Strobe, which periodically sends a message to output port. The only difference is that my message is not an input parameter but is a variable that needs to be periodically calculated. I’m trying to understand how to do it but I didn’t find much information about.

So, this block has no input ports and only one message output port, then the first portion of code should be

class msg_block(gr.sync_block):
   def __init__(self):
       gr.sync_block.__init__(
           self,
           name="msg_block",
           in_sig=None,
           out_sig=None)

       self.message_port_register_out(pmt.intern('msg_out'))

The first issue is that I couldn’t realize even a simple message source. Because if in_sig and out_sig are None, the work method "does not work" then, if I insert the line

self.message_port_pub(pmt.intern('msg_out'), pmt.intern('hello world'))

inside it, it does not really put the message on the msg_out port. In fact, if I run a gnuradio app with my block and a Message debug, nothing is printed. I think I didn’t understand how the method message_port_pub() works because I tried few solution, but none of these worked.

As second step, of course, it would be the introducing of the time loop. I think to use a threading.Timer.

I looked everywhere the message strobe code but did not find it.
Could someone help me to understand how to make both the message source and a message strobe block?

Thanks.