System Laboratories, Inc.(JSL) Company in Nagano Prefecture •Web Engineer •GEEKLAB.NAGANO - Community space management •Valuebooks, inc •Aiming to be a service loved by book lovers (used book purchase and sales) Here is today's code
•Python 3 Engineer Certi fi cation Practice Exam •Use it like a dictionary! • I am responsible for the following chapters • Chapter2 coding rule • Chapter5 Type hints • Chapter19 Concurrency, Parallel Processing
asynchronous processing code •Evolved with each version High level API - very easy to write •I gave such a talk in my book and at PyCon JP 2021. Please do! "4(*ΞϓϦέʔγϣϯೖ͜Θ͘ͳ͍BTZODJPجૅͱඇಉظ*0'BTU"1*Λྫʹ 1Z$PO+1 •Handle multiple tasks concurrent •Effective for I/O-bound processing (e.g., DB access/HTTP requests)
use it. •The synchronous process I'm used to is suf fi cient. •No IO (mostly machine learning and data analysis) (lots of CPU hard work) •Asynchronous processing seems to have unpredictable behavior. •Write in other languages (Go, JS(nodejs/deno...), Rust, C#, Swift, etc.)
behavior. •that's true •Likely to move unpredictably •I don't know what happens when an exception happens. •What happens if I EXCEPT this parallel running task?" •When an exception occurs, what are the other tasks... •A new feature that solves this
(Python 3.10 and earlier) and future (Python 3.11), respectively •Exceptionally easy to write! •This is how cancellations work. •How to write "predictable" and "safe" asyncio •“Hello-ish world” •TaskGroup Let's give it a try.
•Python Core Developer Yury Selivanov tweetʢasync/await Authorʣ •When Taskgroup was MERGE, they were posting a series of excited tweets. •I don't understand it after reading the documentation. •I don't know what's so great about it 🤔
Python, a book that has been a great help to us. •There was a code I didn't understand. •Two big ones. •Quickstart - Example 3-2. The “Hello-ish World” of Asyncio •I would like to revamp this code with asyncio.TaskGroup
(also new except* syntax) •Cancel Task •asyncio's New Hello World •Don't talk. •asyncio basics no more •Speci fi c examples in the application •What's happening at ASGI IUUQTHJUIVCDPNKSGLUBML
scheduled for release on October 3, but is now scheduled for October 24. •Operation is con fi rmed with Python 3.11.0rc2 IUUQTQFQTQZUIPOPSHQFQ •I don't think so, but there is no possibility that asyncio.TaskGroup is a dream function... •This talk is designed to disappear from your mind.
Python 3.10 and earlier. •asyncio.gather() and asyncio.wait() •There are two major features that distinguish it from them asycio.TaskGroup •Catching Concurrent Exceptions •Cancel task when exception occurs
may occur at the same time •Let's see how to capture it in Python 3.10 or earlier •Using the high-level API asyncio.gather() added in Python 3.7 •Options for exceptions to asyncio.gather()ʮreturn_exceptionsʯ •return_exceptions False •return_exceptions True •Simultaneous execution of speci fi ed tasks (asynchronous functions)
be caught Only the fi rst exception is captured The rest are suppressed. async def main(): """return_exceptionsͳ͠""" try: results = await asyncio.gather( coro_success(), coro_value_err(), coro_type_err() ) print(f"{results=}") except ValueError as err: print(f"{err=}") except TypeError as err: print(f”{err=}") asyncio.run(main()) asyncio.gather - return_exceptions False Catching Concurrent Exceptions
asyncio.gather( coro_success(), coro_value_err(), coro_type_err(), return_exceptions=True) print(f"{results=}") results=['ޭ', ValueError(), TypeError()] $ python310 Get all results in a list Need to see what exceptions were raised asyncio.gather - return_exceptions True Catching Concurrent Exceptions
asyncio.gather( coro_success(), coro_value_err(), coro_type_err(), return_exceptions=True) print(f"{results=}") for result in results: match result: case ValueError(): print("ValueError") case TypeError(): print("TypeError") asyncio.gather - return_exceptions True Catching Concurrent Exceptions
asyncio.gather( coro_success(), coro_value_err(), coro_type_err(), return_exceptions=True) print(f"{results=}") results=['ޭ', ValueError(), TypeError()] ValueError() for result in results: match result: case ValueError(): print("ValueError") case TypeError(): print("TypeError") TypeError() asyncio.gather - return_exceptions True Catching Concurrent Exceptions
"""return_exceptions=True͋Γ""" results = await asyncio.gather( coro_success(), coro_value_err(), coro_type_err(), return_exceptions=True) print(f"{results=}") results=['ޭ', ValueError(), TypeError()] ValueError() for result in results: match result: case ValueError(): print("ValueError") case TypeError(): print("TypeError") TypeError() Need to check results All tasks need to be performed Catching Concurrent Exceptions
the same time •Exception occurred in the fi rst task •We'll have to wait until the remaining nine that might fail are complete. (even if all 10 result in the same error) Catching Concurrent Exceptions Python 3.10 and earlier issues •Unable to capture except for the fi rst exception. •Cannot log all exceptions that occur •Need to check the return list. •All tasks must be performed •return_exceptions False •return_exceptions True
capture except for the fi rst exception. •Cannot log all exceptions that occur •Need to check the return list. •All tasks must be performed •return_exceptions False •return_exceptions True •The solution is asyncio.TaskGroup and the new "except*" syntax
= tg.create_task(coro_success()) task2 = tg.create_task(coro_value_err()) task3 = tg.create_task(coro_type_err()) results = [task1.result(), task2.result(), task3.result()] except* ValueError as err: print(f"{err=}") except* TypeError as err: print(f"{err=}") Can be captured by except as a synchronous process Catching Exceptions in asycio.TaskGroup
TypeError as err: print(f"{err=}") except* except* err=ExceptionGroup('unhandled errors in a TaskGroup', [ValueError()]) err=ExceptionGroup('unhandled errors in a TaskGroup', [TypeError()])
syntax •Use with ExceptionGroup (added 3.11) for built-in exception types •ExceptionGroup •Use when you need to raise multiple unrelated exceptions •try except •try except* •ExceptionGroup(“message”, [ValueError(1), TypeError(2)]) new syntax
tb): ... if self._errors: # Exceptions are heavy objects that can have object # cycles (bad for GC); let's not keep a reference to # a bunch of them. errors = self._errors self._errors = None me = BaseExceptionGroup('unhandled errors in a TaskGroup', errors) raise me from None ExceptionGroup
if self._errors: # Exceptions are heavy objects that can have object # cycles (bad for GC); let's not keep a reference to # a bunch of them. errors = self._errors self._errors = None me = BaseExceptionGroup('unhandled errors in a TaskGroup', errors) raise me from None IUUQTHJUIVCDPNQZUIPODQZUIPOCMPCNBJO-JCBTZODJPUBTLHSPVQTQZ asycio.TaskGroup ExceptionGroup
... if self._errors: # Exceptions are heavy objects that can have object # cycles (bad for GC); let's not keep a reference to # a bunch of them. errors = self._errors self._errors = None me = BaseExceptionGroup('unhandled errors in a TaskGroup', errors) raise me from None asycio.TaskGroup ExceptionGroup
654 ྫ֎άϧʔϓͱTaskGroup •https://www.python.jp/news/wnpython311/except-grp.html •The 2021 Python Language Summit: PEP 654 — Exception Groups and except* •https://pyfound.blogspot.com/2021/05/the-2021-python-language-summit-pep-654.html • How Exception Groups Will Improve Error Handling in AsyncIO - Łukasz Langa | Power IT Conference •https://www.youtube.com/watch?v=Lfe2zsGS0Js new syntax except* Born for what?
happens to the remaining tasks that were running at the same time? •In some cases, the remaining tasks are executed as they are. •Let's take asyncio.gather() as an example of a case that remains
raise ValueError async def coro_type_err(): raise TypeError มߋͳ͠ มߋͳ͠ •Add one asynchronous function - wait a bit Preparation - add one asynchronous function
coro_value_err(), coro_long() ) print(f"{results=}") except ValueError as err: print(f"{err=}") except TypeError as err: print(f”{err=}”) print("ऴྃ") asyncio.run(main()) $ python310 4_remaining_tasks.py err=ValueError() ऴྃ ͍ྃͯ͠ͳ͍λεΫ͕ग़ྗ͍ͯ͠·͢ I want to stop. I want to roll back Cases where tasks remain - asyncio.gather - return_exceptions false If an exception occurs Other tasks remain running Hard to predict behavior
try: results = await asyncio.gather( coro_success(), coro_value_err(), coro_long() ) print(f"{results=}") except ValueError as err: print(f"{err=}") except TypeError as err: print(f”{err=}”) print("ऴྃ") asyncio.run(main()) $ python310 4_remaining_tasks.py err=ValueError() ऴྃ ͍ྃͯ͠ͳ͍λεΫ͕ग़ྗ͍ͯ͠·͢ ɾࢭΊ͍ͨ ɾϩʔϧόοΫ͍ͨ͠ ྫ֎͕ൃੜͨ͠߹ ଞͷλεΫಈ͍ͨ·· ಈ࡞Λ༧ଌͮ͠Β͍ I want to stop. I want to roll back If an exception occurs Other tasks remain running Hard to predict behavior
happens to the remaining tasks that were running at the same time? •In some cases, the remaining tasks are executed as they are. •Cancel a task (Cancellations were not added on 3.11) •Cancellation Basics •Cancel when using asyncio.gather() before 3.10 •Let's fi x the process that leaves the task
that leaves the task •Asynchronous function (coro_long()) to be canceled •Instructions to check and cancel remaining tasks •Wait for post-cancellation processing to complete. Added post-processing for cancellations •There are three perspectives for modi fi cation
to the cancelled task •receive asyncio.CancelledError in an asynchronous function •Resend asyncio.CancelledError •I'm a little confused. Let's try to implement it. Added post-processing for cancellations
raise ValueError async def coro_long(): มߋͳ͠ มߋͳ͠ มߋ await asyncio.sleep(1) print("͍ྃͯ͠ͳ͍λεΫ͕ग़ྗ͍ͯ͠·͢") return "ޭʁ" •Therefore, it is necessary to receive asyncio.CancelledError in an asynchronous function •In addition, resend asyncio.CancelledError in an asynchronous function Advance preparation - add post-processing in case of cancellation
it is necessary to receive asyncio.CancelledError in an asynchronous function •In addition, resend asyncio.CancelledError in an asynchronous function Advance preparation - add post-processing in case of cancellation
•Therefore, it is necessary to receive asyncio.CancelledError in an asynchronous function •In addition, resend asyncio.CancelledError in an asynchronous function Advance preparation - add post-processing in case of cancellation
asyncio.CancelledError as err: try: •Therefore, it is necessary to receive asyncio.CancelledError in an asynchronous function •In addition, resend asyncio.CancelledError in an asynchronous function Advance preparation - add post-processing in case of cancellation
asyncio.CancelledError as err: try: print("Ωϟϯηϧ͞ΕͨλεΫ͕ग़ྗ͍ͯ͠·͢") raise asyncio.CancelledError •Therefore, it is necessary to receive asyncio.CancelledError in an asynchronous function •In addition, resend asyncio.CancelledError in an asynchronous function Advance preparation - add post-processing in case of cancellation
that leaves the task •Asynchronous function (coro_long()) to be canceled •Instructions to check and cancel remaining tasks •Wait for post-cancellation processing to complete. Added post-processing for cancellations •There are three perspectives for modi fi cation
that leaves the task •Asynchronous function (coro_long()) to be canceled •Instructions to check and cancel remaining tasks •Wait for post-cancellation processing to complete. Added post-processing for cancellations •There are three perspectives for modi fi cation
and cancel remaining tasks •Determine completion of a task - Task.done() •Wait for post-cancel process to complete - asyncio.sleep() •Let's modify the code.
coro_value_err(), coro_long() ) asyncio.run(main()) print(f"{results=}") except ValueError as err: print(f"{err=}") except TypeError as err: print(f”{err=}”) print("ऴྃ") Cases where tasks remain → Add instructions to con fi rm and cancel tasks Python 3.10 or earlier - asyncio.gather()
asyncio.create_task(coro_value_err()) task3 = asyncio.create_task(coro_long()) results = await asyncio.gather(*[task1, task2, task3]) asyncio.run(main()) print(f"{results=}") except ValueError as err: print(f"{err=}") except TypeError as err: print(f”{err=}”) print("ऴྃ") for task in [task1, task2, task3]: if task.done() is False: Task.done()Ͱ ະྃͷλεΫΛಛఆ Cases where tasks remain → Add instructions to con fi rm and cancel tasks Python 3.10 or earlier - asyncio.gather()
asyncio.create_task(coro_value_err()) task3 = asyncio.create_task(coro_long()) results = await asyncio.gather(*[task1, task2, task3]) asyncio.run(main()) print(f"{results=}") except ValueError as err: print(f"{err=}") except TypeError as err: print(f”{err=}”) for task in [task1, task2, task3]: if task.done() is False: task.cancel() # ະྃͷλεΫΛΩϟϯηϧ ະྃͷλεΫʹର͠ Task.cancel()Λ࣮ߦ print("ऴྃ") Cases where tasks remain → Add instructions to con fi rm and cancel tasks Python 3.10 or earlier - asyncio.gather()
asyncio.create_task(coro_value_err()) task3 = asyncio.create_task(coro_long()) results = await asyncio.gather(*[task1, task2, task3]) asyncio.run(main()) print(f"{results=}") except ValueError as err: print(f"{err=}") except TypeError as err: print(f”{err=}”) for task in [task1, task2, task3]: if task.done() is False: task.cancel() # ະྃͷλεΫΛΩϟϯηϧ ྃͪͷ asyncio.sleep() print("ऴྃ") await asyncio.sleep(1) Cases where tasks remain → Add instructions to con fi rm and cancel tasks Python 3.10 or earlier - asyncio.gather()
asyncio.create_task(coro_value_err()) task3 = asyncio.create_task(coro_long()) results = await asyncio.gather(*[task1, task2, task3]) asyncio.run(main()) print(f"{results=}") except ValueError as err: print(f"{err=}") except TypeError as err: print(f”{err=}”) for task in [task1, task2, task3]: if task.done() is False: task.cancel() # ະྃͷλεΫΛΩϟϯηϧ શମ͜Μͳײ͡ print("ऴྃ") await asyncio.sleep(1) Cases where tasks remain → Add instructions to con fi rm and cancel tasks Python 3.10 or earlier - asyncio.gather()
asyncio.CancelledError as err: try: print("Ωϟϯηϧ͞ΕͨλεΫ͕ग़ྗ͍ͯ͠·͢") raise asyncio.CancelledError •Therefore, it is necessary to receive asyncio.CancelledError in an asynchronous function •In addition, resend asyncio.CancelledError in an asynchronous function Advance preparation - add post-processing in case of cancellation
asyncio.create_task(coro_value_err()) task3 = asyncio.create_task(coro_long()) results = await asyncio.gather(*[task1, task2, task3]) asyncio.run(main()) print(f"{results=}") except ValueError as err: print(f"{err=}") except TypeError as err: print(f”{err=}”) for task in [task1, task2, task3]: if task.done() is False: task.cancel() # ະྃͷλεΫΛΩϟϯηϧ print("ऴྃ") await asyncio.sleep(1) If canceled On the asynchronous function side Catch Cancel $ python310 5_canceling_task_gather.py err=ValueError() Ωϟϯηϧ͞ΕͨλεΫ͕ग़ྗ͍ͯ͠·͢ async def coro_long(): await asyncio.sleep(1) print("͍ྃͯ͠ͳ͍λεΫ͕ग़ྗ͍ͯ͠·͢") return "ޭʁ" except asyncio.CancelledError as err: try: print("Ωϟϯηϧ͞ΕͨλεΫ͕ग़ྗ͍ͯ͠·͢") raise asyncio.CancelledError ऴྃ basic principle of cancellation Cases where tasks remain → Add instructions to con fi rm and cancel tasks Python 3.10 or earlier - asyncio.gather()
that leaves the task •Asynchronous function (coro_long()) to be canceled •Instructions to check and cancel remaining tasks •Wait for post-cancellation processing to complete. Added post-processing for cancellations •There are three perspectives for modi fi cation
are canceled. •Wait for cancellation process to complete. •That's all! •In short, nothing special needs to be done. It will be canceled. Let's refactor the code we just wrote. Cancellation process in asycio.TaskGroup
asyncio.create_task(coro_value_err()) task3 = asyncio.create_task(coro_long()) asyncio.run(main()) print(f"{results=}") for task in [task1, task2, task3]: if task.done() is False: task.cancel() # ະྃͷλεΫΛΩϟϯηϧ print("ऴྃ") await asyncio.sleep(1) Cancellation process in asycio.TaskGroup Let's refactor it. results = await asyncio.gather(*[task1, task2, task3]) except ValueError as err: print(f"{err=}") except TypeError as err: print(f”{err=}”)
asyncio.create_task(coro_value_err()) task3 = asyncio.create_task(coro_long()) asyncio.run(main()) for task in [task1, task2, task3]: if task.done() is False: task.cancel() # ະྃͷλεΫΛΩϟϯηϧ print("ऴྃ") await asyncio.sleep(1) results = await asyncio.gather(*[task1, task2, task3]) print(f"{results=}") except ValueError as err: print(f"{err=}") except TypeError as err: print(f”{err=}”) Cancellation process in asycio.TaskGroup Let's refactor it.
task2, task3]: if task.done() is False: task.cancel() # ະྃͷλεΫΛΩϟϯηϧ print("ऴྃ") await asyncio.sleep(1) async with asyncio.TaskGroup() as g: task1 = asyncio.create_task(coro_success()) task2 = asyncio.create_task(coro_value_err()) task3 = asyncio.create_task(coro_long()) print(f"{results=}") except ValueError as err: print(f"{err=}") except TypeError as err: print(f”{err=}”) Cancellation process in asycio.TaskGroup Let's refactor it.
task2, task3]: if task.done() is False: task.cancel() # ະྃͷλεΫΛΩϟϯηϧ print("ऴྃ") await asyncio.sleep(1) async with asyncio.TaskGroup() as g: task1 = g.create_task(coro_success()) task2 = g.create_task(coro_value_err()) task3 = g.create_task(coro_long()) print(f"{results=}") except ValueError as err: print(f"{err=}") except TypeError as err: print(f”{err=}”) Cancellation process in asycio.TaskGroup Let's refactor it.
•Simply catch exceptions in a conventional way of writing •Cancel without indication •Except* will not spare any concurrent exceptions. •No longer need to be aware of tasks when executing them •How to write "predictable," "safe," and readable asyncio •New “Hello-ish world”
main(): print(f"{time.ctime()} Hello!") await asyncio.sleep(1.0) print(f"{time.ctime()} GoodBye!") The “Hello-ish World” of Asyncio Checking task status Waiting for cancellation process loop = asyncio.get_event_loop() task = loop.create_task(main()) loop.run_until_complete(task) pending = asyncio.all_tasks(loop=loop) for task in pending: task.cancel() group = asyncio.gather(*pending, return_exceptions=True) loop.run_until_complete(group) loop.close()
coro(): print(f"{time.ctime()} Hello!") await asyncio.sleep(1.0) print(f"{time.ctime()} GoodBye!") The “Hello-ish World” of Asyncio Checking task status Waiting for cancellation process async def main(): async with asyncio.TaskGroup() as tg: task = tg.create_task(coro(...)) try: except* BaseException as e: print(f"{e=}") asyncio.run(main())
•Because of external dependence, exceptions are likely to occur. •Easy to write and read •Let's touch TaskGroup. •Exception/cancellation triggers a review of the existing code. •A more comfortable asyncio life
code IUUQTHJUIVCDPNKSGLUBML import asyncio async def main(): try: async with asyncio.TaskGroup() as tg: task1 = tg.create_task(some_coro(...)) task2 = tg.create_task(another_coro(...)) except* BaseException as e: print(f"{e=}") with asyncio.Runner() as runner: runner.run(main()) 3.11 What's New What is asyncio.Runner! For interactive sessions? run multiple times.
•Asynchronous function asyncore, which has actually been around since Python 1.5 •Third-party asynchronous implementation •curio, trio , AnyIO, quattro, etc. … …
•Python 3.11 Preview: Task and Exception Groups - realpython.com •https://realpython.com/python311-exception-groups/ •Python 3.11ͷ৽ػೳ(ͦͷ4ʣPEP 654 ྫ֎άϧʔϓͱTaskGroup •https://www.python.jp/news/wnpython311/except-grp.html •The 2021 Python Language Summit: PEP 654 — Exception Groups and except* •https://pyfound.blogspot.com/2021/05/the-2021-python-language-summit-pep-654.html • How Exception Groups Will Improve Error Handling in AsyncIO - Łukasz Langa | Power IT Conference •https://www.youtube.com/watch?v=Lfe2zsGS0Js
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