Producing messages with the Python SDK

Last updated: October 17, 2026

With the runtime

Publish a message with its URN and payload. The BabelQueue runtime builds the canonical envelope and pushes it to your broker:

from babelqueue import BabelQueue

app = BabelQueue("redis://localhost:6379/0", queue="orders")

app.publish("urn:babel:orders:created", {
    "order_id": 1042,
    "amount": 99.90,
})

With the codec only

If you manage the broker connection yourself, build the envelope with EnvelopeCodec and publish the JSON to your own client:

from babelqueue import EnvelopeCodec

env  = EnvelopeCodec.make("urn:babel:orders:created", {"order_id": 1042, "amount": 99.90})
body = EnvelopeCodec.encode(env)   # -> UTF-8 JSON string
# redis.rpush("queues:orders", body)
#   /  channel.basic_publish(body=body, ...)

The payload above is wrapped in the canonical schema_version: 1 envelope — identical to what every other SDK emits, with meta.lang set to "python":

{
  "job": "urn:babel:orders:created",
  "trace_id": "7b3f9c2a-e41d-4f88-9b2a-1c0d5e6f7a8b",
  "data": { "order_id": 1042, "amount": 99.90 },
  "meta": { "id": "f1e2d3c4-b5a6-4789-90ab-cdef01234567", "queue": "orders", "lang": "python", "schema_version": 1, "created_at": 1749132727000 },
  "attempts": 0
}

Extension (meta) keys

Pass your own meta keys to EnvelopeCodec.make with the keyword-only meta= argument:

env = EnvelopeCodec.make(
    "urn:acme:orders:created", {"order_id": 1042},
    queue="orders", meta={"ext": {"acme": {"tier": "gold"}}},
)

A key that collides with a core meta key (id, queue, lang, schema_version, created_at) or with a forbidden key (max_retries, attempts, source, ts) raises EnvelopeKeyError; pointer names the key, for example /meta/ts. EnvelopeCodec.encode raises the same error for an envelope that still carries a forbidden key or the inbound-only urn alias, instead of dropping it.

Keep vendor data under a single meta.ext.<vendor> block and use snake_case keys (ADR-0031). The entries are written next to the core meta keys and survive every retry, dead-letter and redrive hop. See Extension keys in the envelope spec.

Next: Consuming messages.