Thanks for the details — this is a known incompatibility between Prefect 3.4.0’s notifications module and newer versions of the Apprise library. What’s happening - Prefect’s notifications module tries to extend Apprise’s NOTIFY_TYPES like

NOTIFY_TYPES += (...)

. - Newer Apprise versions changed

NOTIFY_TYPES

to a

frozenset

(immutable), so the

+=

throws

TypeError: unsupported operand type(s) for +=: 'frozenset' and 'tuple'

. Also, a quick naming note: in Prefect 3.x the class is

PagerDutyWebHook

(capital H) and there is no

PagerDutyWebhookBlock

class name. Loading the block should look like this:

from prefect.blocks.notifications import PagerDutyWebHook

pd = PagerDutyWebHook.load("my-pager-duty-block")

How to fix - Best fix: upgrade to the latest Prefect 3.4.x, which includes multiple compatibility improvements and bugfixes. -

pip install -U prefect

- Release notes: Prefect releases - If you need to stay on Prefect 3.4.0: pin Apprise to an earlier version where

NOTIFY_TYPES

was still mutable. I don’t want to guess the exact version without your environment details — could you share

pip show apprise

? I can confirm a safe pin once I know the version you’re on. Reference docs - Blocks in Prefect 3: Blocks concept docs If you upgrade Prefect and still see the error, let me know your Apprise version and I’ll suggest a precise pin.

Thanks — that traceback is caused by a change in the Apprise library: in newer Apprise versions,

NOTIFY_TYPES

is a frozenset (immutable), and Prefect 3.4.0’s notifications module tries to extend it with

+=

, which raises the TypeError you’re seeing. Also, a quick naming fix: in Prefect 3.x the class is

PagerDutyWebHook

(capital H), and you load it directly from the class (there’s no

PagerDutyWebhookBlock

class). For example:

from prefect.blocks.notifications import PagerDutyWebHook

pd = PagerDutyWebHook.load("my-pager-duty-block")

You’re on Apprise 1.9.5. Here are two ways to get unblocked: - Option A: Upgrade Prefect to the latest 3.4.x - This includes various compatibility improvements and may avoid this issue. - Command:

pip install -U prefect

- Releases: Prefect releases - Option B: Pin Apprise below 1.9.5 (roll back the change that made

NOTIFY_TYPES

immutable) - Command:

pip install "apprise<1.9.5"

- If you still hit the error, try an earlier minor series:

pip install "apprise>=1.8,<1.9"

Docs for reference: Blocks in Prefect 3 Give one of those a try and let me know if the error persists. If you prefer not to change Prefect right now, pinning Apprise below 1.9.5 is the quickest workaround.