asyncio.Task.print_stack doesn't print the full stack

[amit7itz]

BPO	39060
Nosy	@terryjreedy, @asvetlov, @cjerdonek, @1st1, @amit7itz
Files	example.py: An example script that re-produces the bug.

^{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 = None
created_at = <Date 2019-12-16.09:51:58.900>
labels = ['3.8', 'type-bug', '3.7', '3.9', 'expert-asyncio']
title = "asyncio.Task.print_stack doesn't print the full stack"
updated_at = <Date 2020-05-19.01:04:50.216>
user = 'https://github.com/amit7itz'

bugs.python.org fields:

activity = <Date 2020-05-19.01:04:50.216>
actor = 'chris.jerdonek'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['asyncio']
creation = <Date 2019-12-16.09:51:58.900>
creator = 'amit7itz'
dependencies = []
files = ['48779']
hgrepos = []
issue_num = 39060
keywords = []
message_count = 5.0
messages = ['358468', '358474', '358475', '358736', '358792']
nosy_count = 5.0
nosy_names = ['terry.reedy', 'asvetlov', 'chris.jerdonek', 'yselivanov', 'amit7itz']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue39060'
versions = ['Python 3.7', 'Python 3.8', 'Python 3.9']

[amit7itz]

Hi!
I think I found some issue in the "print_stack()" function of asyncio.Task.
When I try to print the stack of some task, I only see the first few lines of the stack.
Attached an example file, that contains a recursive function that after 10 calls prints the stack of the task.
You can see that the stack that it prints only shows the first call of the recursive function, although you would expect to see it 10 times.

Tested on python3.7 and 3.8 on both MacOS and CentOS, the result is the same.

Your help will be appreciated very much! :)

[asvetlov]

Technically the output is correct: a stack for async function call doesn't contain the outer async function that is used for awaiting.

Agree, it may sound confusing, but await f() is not the same as just f().

Perhaps we can provide *alternative* API for retrieving async call stack.

[amit7itz]

In is mainly confusing because I expected this function to behave like "traceback.print_stack()", which prints the stack including all the awaits that lead to it.

[terryjreedy]

Amit, is there a simple doc change that would have made the result clearer? (before getting Andrew's response?)

[amit7itz]

Hi Terry,
I guess the right place to update the Task.get_stack doc: https://docs.python.org/3/library/asyncio-task.html#asyncio.Task.get_stack

I'm not sure I know the terminology enough to phrase it right, but I would add there something like:
Note that the task's stack does not include the stack of coroutines that were awaited inside the task, as it is not part of the Task itself.

But I am sure one of you can phrase it more professionally than me :)