asyncio Task._fut_waiter done callback

[ghost]

BPO	37281
Nosy	@asvetlov, @1st1

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2019-06-14.11:15:23.540>
created_at = <Date 2019-06-14.10:32:18.328>
labels = ['type-bug', '3.7', 'expert-asyncio']
title = 'asyncio Task._fut_waiter done callback'
updated_at = <Date 2019-06-14.11:15:23.539>
user = None

bugs.python.org fields:

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components = ['asyncio']
creation = <Date 2019-06-14.10:32:18.328>
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issue_num = 37281
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priority = 'normal'
resolution = None
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue37281'
versions = ['Python 3.7']

[ghost]

Future has a done_callback, but Task not, why ?
Is a safe to use Task._fut_waiter future done_callback?

[asvetlov]

1. Task._fut_waiter is a private API, please avoid it
2. Task class is derived from Future, thus it HAS add_done_callback() method. The other question is that from my experience if the application-level code uses add_done_callback() the design is not perfect and error-prone. add_done_callback() is useful for relatively low-level libraries.

[ghost]

Sorry, you right! But why not set_result and set_exception?
My code: waiter_task.add_done_callback(lambda f: f.result()) because i don't wont to store my running tasks in the array but i must query awaiteable for the result.
Thank you for a reply.

[asvetlov]

See bpo-32363

[ghost]

Thanks