6_union.py

from typing import Literal, TypedDict, Union


class NewJobEvent(TypedDict):
    tag: Literal["new-job"]
    job_name: str
    config_file_path: str


class CancelJobEvent(TypedDict):
    tag: Literal["cancel-job"]
    job_id: int

# Old syntax
#Event = Union[NewJobEvent, CancelJobEvent] 

# New syntax
Event = NewJobEvent | CancelJobEvent # new syntax


def process_event(event: Event) -> None:
    # Since we made sure both TypedDicts have a key named 'tag', it's
    # safe to do 'event["tag"]'. This expression normally has the type
    # Literal["new-job", "cancel-job"], but the check below will narrow
    # the type to either Literal["new-job"] or Literal["cancel-job"].
    #
    # This in turns narrows the type of 'event' to either NewJobEvent
    # or CancelJobEvent.
    if event["tag"] == "new-job":
        print(event["job_name"])
    else:
        print(event["job_id"])