Skip upstream tasks in a (recurring) scheduled flow

[ReubenTheDS]

This info is for anyone who might have questions on skipping upstream tasks in a scheduled flow:
For upstream tasks specifically, see my previous question on "set_dependencies"

Now, let's say you have a flow with 4 tasks scheduled to run every 5 hours. Your pseudocode might be:

from prefect import task, Flow
from prefect.schedules import IntervalSchedule
import pendulum
from prefect.engine import signals
from datetime import datetime, timedelta


@task(log_stdout=True)
def task_1():
    print("In task1")
    #create some files
    return 1


@task(log_stdout=True)
def task_2(val_1):
    print("In task2")
    print("val1: {}".format(val_1))
    return 2


@task(log_stdout=True)
def task_3(val_1, val_2):
    print("In task3")
    print("val1: {}, val_2:{}".format(val_1, val_2))
    return 3


@task(log_stdout=True)
def task_4():
    print("In task4")


# define a schedule for Prefect's flow
schedule = IntervalSchedule(
        start_date=datetime.utcnow() + timedelta(seconds=1),
        interval=timedelta(hours=5))

with Flow("Template") as flow:
    t1 = task_1() # task 1 generates files( this will take time ) as well as returns something
    t2 = task_2( t1 ) # and I want task_2 to run only after task_1 is completed, since it will read the files generated
    t3 = task_3( t1, t2 ) # and I want task_3 to run only after task_2 is completed, for reason X
    t4 = task_4()  # wait for all above tasks to finish, without passing t1, t2 or t3

    t4.set_upstream(t1)
    t4.set_upstream(t2)
    t4.set_upstream(t3)
    # or t4.set_upstream([t1, t2, t3])

Now, if for example, task_2 fails, and you want to skip task_3 & task_4 in this flow run, but have them all run ( as usual ) in the next flow run 5 hours later, modify task_2:

@task(log_stdout=True)
def task_2(val_1):
    print("In task2")

    if some_condition:
        raise signals.FAIL

    print("val1: {}".format(val_1))
    return 2

To the gurus out here, as usual, if there's a mistake, or a better/more concise way, please correct me :)