On 26/04/15 23:24, Nick Coghlan wrote:
>
> On 27 Apr 2015 07:50, "Mark Shannon" <mark at hotpy.org
> <mailto:mark at hotpy.org>> wrote:
> > On 26/04/15 21:40, Yury Selivanov wrote:
> >>
> >> But it's hard. Iterating through something asynchronously? Write a
> >> 'while True' loop. Instead of 1 line you now have 5 or 6. Want to
> >> commit your database transaction? Instead of 'async with' you will
> >> write 'try..except..finally' block, with a very high probability to
> >> introduce a bug, because you don't rollback or commit properly or
> >> propagate exception.
> >
> > I don't see why you can't do transactions using a 'with' statement.
>
> Because you need to pass control back to the event loop from the
> *__exit__* method in order to wait for the commit/rollback operation
> without blocking the scheduler. The "with (yield from cm())" formulation
> doesn't allow either __enter__ *or* __exit__ to suspend the coroutine to
> wait for IO, so you have to do the IO up front and return a fully
> synchronous (but still non-blocking) CM as the result.
True. The 'with' statement cannot support this use case, but
try-except can do the job:
trans = yield from db_conn.transaction()
try:
...
except:
yield from trans.roll_back()
raise
yield from trans.commit()
Admittedly not as elegant as the 'with' statement, but perfectly readable.
>
> We knew about these problems going into PEP 3156
> (http://python-notes.curiousefficiency.org/en/latest/pep_ideas/async_programming.html#using-special-methods-in-explicitly-asynchronous-code)
> so it's mainly a matter of having enough experience with asyncio now to
> be able to suggest specific syntactic sugar to make the right way and
> the easy way the same way.
asyncio is just one module amongst thousands, does it really justify
special syntax?
Cheers,
Mark.
RetroSearch is an open source project built by @garambo | Open a GitHub Issue
Search and Browse the WWW like it's 1997 | Search results from DuckDuckGo
HTML:
3.2
| Encoding:
UTF-8
| Version:
0.7.4