Path: csiph.com!fu-berlin.de!uni-berlin.de!not-for-mail From: "Frank Millman" Newsgroups: comp.lang.python Subject: Re: Cannot step through asynchronous iterator manually Date: Sat, 30 Jan 2016 10:22:20 +0200 Lines: 57 Message-ID: References: Mime-Version: 1.0 Content-Type: text/plain; format=flowed; charset="iso-8859-1"; reply-type=original Content-Transfer-Encoding: 7bit X-Trace: news.uni-berlin.de zGGKGYKkUt/CX8yErwJm7gtdNB4Ek/6UzoBXAQxPFjEQ== Return-Path: X-Original-To: python-list@python.org Delivered-To: python-list@mail.python.org X-Spam-Status: OK 0.001 X-Spam-Evidence: '*H*': 1.00; '*S*': 0.00; 'else:': 0.03; 'higher- level': 0.09; 'loop.': 0.09; 'received:80.91': 0.09; 'received:80.91.229': 0.09; 'received:gmane.org': 0.09; 'received:list': 0.09; 'rows': 0.09; 'python': 0.10; 'jan': 0.11; 'exception': 0.13; '...)': 0.16; '2016': 0.16; 'async': 0.16; 'iterator': 0.16; 'iterator,': 0.16; 'iterator.': 0.16; 'received:80.91.229.3': 0.16; 'received:io': 0.16; 'received:plane.gmane.org': 0.16; 'received:psf.io': 0.16; 'returned,': 0.16; 'row': 0.16; 'skip:n 70': 0.16; 'wrote:': 0.16; 'case.': 0.18; 'try:': 0.18; 'suggested': 0.20; 'pass': 0.22; 'select': 0.23; 'wrote': 0.23; 'header:In-Reply-To:1': 0.24; 'discussion': 0.24; 'header:X-Complaints-To:1': 0.26; "skip:' 10": 0.28; 'raise': 0.29; 'usually': 0.33; 'except': 0.34; 'exist': 0.35; 'expected': 0.35; 'step': 0.36; 'but': 0.36; 'there': 0.36; 'to:addr:python-list': 0.36; 'pm,': 0.36; 'subject:: ': 0.37; 'received:org': 0.37; 'desired': 0.37; 'missing': 0.37; 'test': 0.39; 'does': 0.39; 'to:addr:python.org': 0.40; 'entire': 0.61; 'more': 0.63; 'times': 0.63; 'statement,': 0.66; 'course.': 0.67; 'liked': 0.67; 'frank': 0.72; 'special': 0.73; "'for'": 0.84; 'chrisa': 0.84; 'construct': 0.84 X-Injected-Via-Gmane: http://gmane.org/ X-Gmane-NNTP-Posting-Host: 197.86.205.12 In-Reply-To: X-MSMail-Priority: Normal Importance: Normal X-Newsreader: Microsoft Windows Live Mail 15.4.3502.922 X-MimeOLE: Produced By Microsoft MimeOLE V15.4.3502.922 X-BeenThere: python-list@python.org X-Mailman-Version: 2.1.20+ Precedence: list List-Id: General discussion list for the Python programming language List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Xref: csiph.com comp.lang.python:102287 "Ian Kelly" wrote in message news:CALwzid=sSDSm8hdAN+ORJ54A_jEu9Wc8103iqGKAah8mrj-TXw@mail.gmail.com... > On Jan 29, 2016 11:04 PM, "Frank Millman" wrote: > > > > Hi all > > > > To loop though an iterator one usually uses a higher-level construct > > such as a 'for' loop. However, if you want to step through it manually you can do so with next(iter). > > > > I expected the same functionality with the new 'asynchronous iterator' > > in Python 3.5, but I cannot find it. > > > > I can achieve the desired result by calling 'await aiter.__anext__()', but this is clunky. > > > > Am I missing something? > > async for x in aiter: > pass > > Can only be used inside a coroutine, of course. I know that you can use this to loop through the entire iterator, but I have a special case. There are times when I want to execute a SELECT statement, and test for three possibilities - - if no rows are returned, the object does not exist - if one row is returned, the object does exist - if more that one row is returned, raise an exception We had a recent discussion about the best way to do this, and ChrisA suggested the following, which I liked - cur.execute('SELECT ...) try: row = next(cur) except StopIteration: # row does not exist else: try: next_row = next(cur) except StopIteration: # row does exist else: # raise exception Now that I have gone async, I want to do the same with an asynchronous iterator. Frank