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gh-101581 Optionally prevent child tasks from being cancelled in asyncio taskgroups #101648

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gh-101581 Optionally prevent child tasks from being cancelled in asyncio taskgroups #101648

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2df96d0
add `defer_errors` flag to `asyncio.TaskGroup`
DontPanicO Feb 7, 2023
90e58aa
tests for `asyncio.TaskGroup` with `defer_errors=True`
DontPanicO Feb 7, 2023
0b08887
Add `NEWS.d` entry
DontPanicO Feb 7, 2023
bb09126
Merge remote-tracking branch 'upstream/main' into asyncio_taskgroup_d…
DontPanicO Mar 17, 2023
481d372
Update `asyncio.TaskGroup` docstring
DontPanicO Mar 17, 2023
62d8246
Merge branch 'main' into asyncio_taskgroup_dont_abort_on_exception
willingc Apr 26, 2023
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15 changes: 10 additions & 5 deletions Lib/asyncio/taskgroups.py
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Original file line number Diff line number Diff line change
Expand Up @@ -23,9 +23,11 @@ class TaskGroup:

Any exceptions other than `asyncio.CancelledError` raised within
a task will cancel all remaining tasks and wait for them to exit.
You can prevent this behavior by passing `defer_errors=True` to
the constructor.
The exceptions are then combined and raised as an `ExceptionGroup`.
"""
def __init__(self):
def __init__(self, defer_errors=False):
self._entered = False
self._exiting = False
self._aborting = False
Expand All @@ -36,6 +38,7 @@ def __init__(self):
self._errors = []
self._base_error = None
self._on_completed_fut = None
self._defer_errors = defer_errors

def __repr__(self):
info = ['']
Expand Down Expand Up @@ -198,7 +201,8 @@ def _on_task_done(self, task):
return

self._errors.append(exc)
if self._is_base_error(exc) and self._base_error is None:
is_base_error = self._is_base_error(exc)
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Hi @DontPanicO, I'm trying to understand why is_base_error is needed. Please help me understand why that is preferable to self._is_base_error(exc). Thanks!

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Hi @willingc . I stored self._is_base_error(exc) result in a variable since it's used twice: once on line 205 and once on line 238

if is_base_error and self._base_error is None:
self._base_error = exc

if self._parent_task.done():
Expand Down Expand Up @@ -231,6 +235,7 @@ def _on_task_done(self, task):
# pass
# await something_else # this line has to be called
# # after TaskGroup is finished.
self._abort()
self._parent_cancel_requested = True
self._parent_task.cancel()
if not self._defer_errors or is_base_error:
self._abort()
self._parent_cancel_requested = True
self._parent_task.cancel()
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