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

[Anisha Gorur]

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....

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?
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?
Thank You,

-Anisha