Path: csiph.com!news.swapon.de!fu-berlin.de!uni-berlin.de!not-for-mail From: Oscar Benjamin Newsgroups: comp.lang.python Subject: Re: yield in try/finally case Date: Thu, 3 Mar 2016 16:24:38 +0000 Lines: 55 Message-ID: References: <84965b86-819b-4924-bca9-e82eed040606@googlegroups.com> <1457017939.1829117.538575946.054CBB8F@webmail.messagingengine.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 X-Trace: news.uni-berlin.de eMHjcm4PB7DSY1IQIibGNgW5Up9UY8CNDk1Ip8tF2h8A== Return-Path: X-Original-To: python-list@python.org Delivered-To: python-list@mail.python.org X-Spam-Status: OK 0.004 X-Spam-Evidence: '*H*': 0.99; '*S*': 0.00; 'anyway.': 0.04; 'context': 0.05; 'sys': 0.05; 'exit': 0.07; 'pypy': 0.07; 'cc:addr:python- list': 0.09; 'exit.': 0.09; 'lambda:': 0.09; 'def': 0.13; 'explicitly': 0.15; "hasn't": 0.15; 'thu,': 0.15; '2016': 0.16; '__del__': 0.16; 'cc:name:python list': 0.16; 'hams': 0.16; 'received:io': 0.16; 'received:psf.io': 0.16; 'subject:case': 0.16; 'subject:yield': 0.16; 'wrote:': 0.16; 'cc:2**0': 0.20; 'cc:addr:python.org': 0.20; 'either.': 0.22; 'import': 0.24; 'header:In-Reply-To:1': 0.24; "doesn't": 0.26; 'message- id:@mail.gmail.com': 0.27; 'yield': 0.27; 'skip:u 20': 0.28; '---': 0.28; 'subject:/': 0.30; 'code': 0.30; 'supposed': 0.31; 'probably': 0.31; 'run': 0.33; 'point': 0.33; 'achieving': 0.33; 'foo': 0.33; 'open': 0.33; 'file': 0.34; 'received:google.com': 0.35; 'done': 0.35; 'but': 0.36; 'received:209.85': 0.36; "wasn't": 0.36; 'subject:: ': 0.37; 'received:209': 0.38; 'files': 0.38; 'end': 0.39; 'why': 0.39; 'your': 0.60; 'close': 0.61; "you'll": 0.61; 'skip:u 10': 0.61; 'fire': 0.63; 'march': 0.64; 'mar': 0.65; '**kw)': 0.84; '**kw):': 0.84; 'assertion.': 0.84; 'oscar': 0.84; 'otten': 0.84; 'subject:try': 0.84; 'reasoning': 0.91 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc; bh=Kie4zLBkOUpusYqIAqIs7WZsMclsH5ydfZea0v+MiQs=; b=opMFx6rd65XZE6UyO/owC6ZcP6226VwndfcMoeWiPR+pMyd4o6h/lwPxc7NzwrBcGd jayMbg3XUS1vinidmblKzlSVFYUKJSTbyvYoLsJ1aOsxEBoYnw+swbX73sko9hlnIxuj c8VGjXdyk+cQug/TZb9/v2bIO+8ab8+e5CXGo+csTcqDUuGmnk2byGiERnaTn9HM5vWd 6fx90W5BsdCC4HE+ePcUNijATfKAGRN+jVF5dNaY49oujphzW4P3QKsiPjPkZc4111kK qDo0WJUDNQz8BHk/sMrUgArwBRVJScQ5ZqnLCNL/eeMXqlB5AYKxOFFe2mqq/sh4WJAr 9Kww== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:to:cc; bh=Kie4zLBkOUpusYqIAqIs7WZsMclsH5ydfZea0v+MiQs=; b=N8ng+Z3O3aiRKc1APfsEySMA4XRsIMtMVbpdonNR2tGj7CNcNjyKvJWbuxc+4Y2zQ+ ZNPmQ0nawajqh6MGZ3bVCocZ6FAfgo5kobni00DM2itvMHy1AJBECr/NvjDIgchFyK2B b9U2hbGnsgCO7Wtt8U6WqAsMxJbXS9gXcI+TB5a6y4lFjomZVtuW6YZp+ZQxY7Dr/uDI IUWeb3iHlxsT3P4lXYPsUT4sZvWt3y2ZGGZ1anNbS82/B3cXRfb3zn1ASmX/KqWCn3oP 6Vdq/aEu6UTaEQaNfzHZ+qYRE3rs7mBQ5RAlxUxg160OP0mPocOG/8z29Ls9y+wS6rHk zEHQ== X-Gm-Message-State: AD7BkJLkSJy6+06PoDrNCaB0ei6avV5l/Iu6Q+0N2Tce9EURlee0HOtuomNk0MyF2t5JHtG//ejtqUO9Fo3Phg== X-Received: by 10.112.235.71 with SMTP id uk7mr1340370lbc.39.1457022297896; Thu, 03 Mar 2016 08:24:57 -0800 (PST) In-Reply-To: <1457017939.1829117.538575946.054CBB8F@webmail.messagingengine.com> X-BeenThere: python-list@python.org X-Mailman-Version: 2.1.21 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:103975 On 3 March 2016 at 15:12, Random832 wrote: > On Thu, Mar 3, 2016, at 08:47, Peter Otten wrote: >> This is because the last generator uf = upperfile(...) is not garbage- >> collected and wasn't explicitly closed either. > > But the program hasn't ended yet when you run your assertion. > > import sys > > _open = open > files = [] > > def myclose(self): > print("--- closed " + self.name) > self._close() > > def open(*args, **kw): > f = _open(*args, **kw) > f._close = f.close > f.close = lambda: myclose(f) > files.append(f) > return f > > def upperfile(filename): > with open(filename) as f: > for line in f: > yield line.upper() > > for uf in map(upperfile, sys.argv[1:]): > for line in uf: > print(line, end="") > break > > print("--- end of program") > > ==== > > FOO > --- closed tmp1.txt > HAMS > --- end of program > --- closed tmp2.txt If you're happy letting __del__ close the file then why bother with the context manager in the first place? By the reasoning above we don't even need to close the file in __del__ since all open files get closed at process exit anyway. The point is that finally/__exit__ are not achieving what they are supposed to achieve: the guarantee that the file is immediately closed when you're done with it. Try your code under pypy and you'll probably find that your context manager doesn't fire even at process exit. -- Oscar