Ifelse introduces Merge task in visualization and flow in 0.10.2

Description

A clear description of the bug

Version 0.10.2 – and carried into 0.10.3 – introduced an explicit Merge in the visualization.

Expected Behavior

What did you expect to happen instead?

I expected a single Merge as I defined it as merged_result:

Tested in 0.9.8 and 0.10.1:

Reproduction

A minimal example that exhibits the behavior.

Given this code:

from prefect import task, Flow
from prefect.tasks.control_flow import ifelse, merge

@task
def poll_for_new_records():
    pass

@task
def is_poll_result_empty(polled_data):
    if polled_data:
        return True
    else:
        return False

@task
def skip_right_past_it_all():
    pass

@task
def extract():
    pass

@task
def transform(payload):
    pass

@task
def load(payload):
    pass

with Flow("Test ETL") as flow:

    p = poll_for_new_records()

    e = extract()
    ifelse(is_poll_result_empty(p), skip_right_past_it_all, e)

    t = transform(e)
    l = load(t)

    merged_result = merge(skip_right_past_it_all, l)

flow.visualize()

Environment

Any additional information about your environment Anaconda, with an environment of Python 3.7, and Prefect 0.9.1 through 0.10.3 tested.

Optionally run prefect diagnostics from the command line and paste the information here { “config_overrides”: {}, “env_vars”: [], “system_information”: { “platform”: “Windows-10-10.0.18362-SP0”, “prefect_version”: “0.10.3”, “python_version”: “3.7.7” } }

[staylorx]

Happy to help @cicdw and @jcrist if/when I can. My team and I have really glommed on to this tool; thank you for the hard work and rapid turnaround.

[dojeda]

Thanks for the quick responses by the prefect team and collaborators!