Re: [Discuss-gnuradio] Read/Write stream tags in Python

[Josh Blum]

On 07/13/2012 08:51 AM, Anisha Gorur wrote:
> Hello all,
> I've been trying to work with stream tags in python, mainly using the
> grextras blocks coding guide
> here:https://github.com/guruofquality/grextras/wiki/Blo...
> <https://github.com/guruofquality/grextras/wiki/Blocks-Coding-Guide#wiki-the-work-function>.
> 
> I've set up a very simple flow graph, just a vector source, throttle and
> file sink, and I would like to place a tag on the first element of the
> vector that contains time metadata. I'm using this code:
> 
> def work(self, input_items, output_items):
> item_index = ? #which output item gets the tag?

set item_index to x so the tag gets associated with outputs_items[0][x]

> offset = self.nitems_written(0) + item_index
> key = pmt.pmt_string_to_symbol("example_key")
> value = pmt.pmt_string_to_symbol("example_value")
> 
> #write at tag to output port 0 with given absolute item offset
> self.add_item_tag(0, offset, key, value)
> 
> I think the problem has something to do with not implementing the
> correct modules. My question is, what are the appropriate modules to
> import to read and write stream tags in python?
> 

You might want to look more that that coding guide, at lot of the
snippets are just work functions, but many contain full class
definitions with import statements. For example:

from gnuradio import gr
import gnuradio.extras

class my_sync_block(gr.block):

    def __init__(self, args):
        gr.block.__init__(self, name="my block", in_sig=[numpy.int32],
out_sig=[numpy.int32])

    def work(self, input_items, output_items):
        #work stuff...
        return len(output_items[0])

-josh