Path: csiph.com!fu-berlin.de!uni-berlin.de!not-for-mail From: Cameron Simpson Newsgroups: comp.lang.python Subject: Re: Try: rather than if : Date: Tue, 15 Dec 2015 17:11:19 +1100 Lines: 58 Message-ID: References: Reply-To: python-list@python.org Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit X-Trace: news.uni-berlin.de CmI5iHiO46lpgorGTgYpHAIAuithmlzRHnhE5intltjQ== Return-Path: X-Original-To: python-list@python.org Delivered-To: python-list@mail.python.org X-Spam-Status: OK 0.000 X-Spam-Evidence: '*H*': 1.00; '*S*': 0.00; 'else:': 0.03; 'none:': 0.05; 'smallest': 0.07; 'cc:addr:python-list': 0.09; '%s\\n"': 0.09; 'attribute.': 0.09; 'logic': 0.09; 'name)': 0.09; 'name):': 0.09; 'def': 0.13; '>on': 0.16; '>try:': 0.16; 'accesses': 0.16; 'attribute,': 0.16; 'dropping': 0.16; 'emit': 0.16; 'fetches': 0.16; 'from:addr:cs': 0.16; 'from:addr:zip.com.au': 0.16; 'from:name:cameron simpson': 0.16; 'message-id:@cskk.homeip.net': 0.16; 'received:io': 0.16; 'received:psf.io': 0.16; 'simpson': 0.16; 'try/except': 0.16; 'wrote:': 0.16; 'attribute': 0.18; 'try:': 0.18; '2015': 0.20; 'cc:2**0': 0.20; 'cc:addr:python.org': 0.20; 'first,': 0.20; 'issue.': 0.20; 'suggested': 0.20; 'cheers,': 0.22; 'pass': 0.22; 'code,': 0.23; 'bit': 0.23; 'dec': 0.23; 'header:In-Reply-To:1': 0.24; 'mon,': 0.24; 'header:User- Agent:1': 0.26; '14,': 0.27; 'this.': 0.28; 'raise': 0.29; 'code': 0.30; 'putting': 0.30; 'probably': 0.31; 'skip:_ 10': 0.32; 'possibly': 0.32; 'class': 0.33; 'case,': 0.34; 'except': 0.34; 'handle': 0.34; 'but': 0.36; 'should': 0.36; 'possible': 0.36; 'pm,': 0.36; 'subject:: ': 0.37; 'two': 0.37; 'say': 0.37; 'things': 0.38; 'version': 0.38; 'received:localdomain': 0.38; 'names': 0.38; 'stuff': 0.38; 'someone': 0.38; 'your': 0.60; 'needing': 0.63; 'cameron': 0.66; 'intent': 0.66; 'header:Reply- To:1': 0.67; 'reply-to:no real name:2**0': 0.71; 'clearer': 0.84; 'reply-to:addr:python.org': 0.84 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) 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:100447 On 14Dec2015 16:48, Vincent Davis wrote: >On Mon, Dec 14, 2015 at 4:14 PM, Cameron Simpson wrote: > >> First, notice that the code inside the try/except _only_ fetches the >> attribute. Your version calls the "write" attribute, and also accesses >> handle.name. Either of those might also emit AttributeError, and should >> probably not be silently caught. >> > >​I think the intent of the original code was to check if handle had the >attribute "name", I don't think the attribute "write" was the issue. I have to say that this was not at all evident to me. I think that also argues for putting the smallest possible bit of code inside the try/except. >So then possibly this based on your suggestion: >try: > write = handel.write >except AttributeError: > raise Someone has already suggested dropping the try/except altogether for this. >try: > name = handel.name > write("# Report_file: %s\n" % name) >except AttributeError: > pass Again, I would minimise the stuff in the try/except, so: try: name = handle.name except AttributeError: pass else: write("# Report_file: %s\n" % name) But in this case, in my code, I do two things: Firstly, things needing names always get one: class Foo: def __init__(self, blah, name=None): if name is None: name = "Foo-%s" % (id(self),) self.name = name Secondly, for your use case "print the name if it has one" I _would_ use hasattr: if hasattr(handle, name): write("# Report_file: %s\n" % name) The logic feels far clearer to my eye. Cheers, Cameron Simpson