Path: csiph.com!eternal-september.org!feeder.eternal-september.org!border1.nntp.ams1.giganews.com!nntp.giganews.com!newsfeed.xs4all.nl!newsfeed7.news.xs4all.nl!newsgate.cistron.nl!newsgate.news.xs4all.nl!post.news.xs4all.nl!not-for-mail 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; 'error:': 0.05; 'python3': 0.05; 'subject:getting': 0.07; 'received:80.91': 0.09; 'received:80.91.229': 0.09; 'received:gmane.org': 0.09; 'received:list': 0.09; 'skip:= 70': 0.10; 'exception': 0.13; 'argument': 0.15; 'argparse': 0.16; 'commandline': 0.16; 'function?': 0.16; 'parameter:': 0.16; 'received:80.91.229.3': 0.16; 'received:dip0.t-ipconnect.de': 0.16; 'received:plane.gmane.org': 0.16; 'received:t-ipconnect.de': 0.16; 'subject:exception': 0.16; 'subject:when': 0.16; 'wrote:': 0.16; 'later': 0.16; 'have:': 0.18; ';-)': 0.18; 'arguments': 0.22; 'parser': 0.22; 'suppose': 0.22; 'import': 0.24; 'header:User- Agent:1': 0.26; "doesn't": 0.26; 'header:X-Complaints-To:1': 0.26; 'least': 0.27; 'correct': 0.28; 'cat': 0.29; 'way?': 0.29; 'raise': 0.29; 'skip:. 10': 0.32; 'handle': 0.34; 'add': 0.34; 'skip:p 30': 0.35; 'there': 0.36; 'to:addr:python-list': 0.36; 'subject:: ': 0.37; 'received:org': 0.37; 'why': 0.39; 'to:addr:python.org': 0.40; 'received:de': 0.40; 'more': 0.63; 'choose': 0.68; "'all'": 0.84; 'cecil': 0.84; 'westerhof': 0.84; 'subject:this': 0.85 X-Injected-Via-Gmane: http://gmane.org/ To: python-list@python.org From: Peter Otten <__peter__@web.de> Subject: Re: Is this a correct way to generate an exception when getting a wrong parameter Date: Wed, 12 Aug 2015 11:33:04 +0200 Organization: None References: <87h9o46flw.fsf@Equus.decebal.nl> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7Bit X-Gmane-NNTP-Posting-Host: p57bd80fc.dip0.t-ipconnect.de User-Agent: KNode/4.13.3 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: , Newsgroups: comp.lang.python Message-ID: Lines: 49 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1439371995 news.xs4all.nl 2922 [2001:888:2000:d::a6]:45141 X-Complaints-To: abuse@xs4all.nl Xref: csiph.com comp.lang.python:95278 Cecil Westerhof wrote: > I have: > ======================================================================== > accepted_params = { > 'pcpu', > 'rss', > 'size', > 'time', > 'vsize', > } > ======================================================================== > > Later I use: > ======================================================================== > if (to_check != 'all') and not(to_check in accepted_params): > raise Exception('Used illegal parameter: {0}.\n' > 'Accepted ones: {1}' > .format(to_check, sorted(accepted_params))) > ======================================================================== > > When using 'all' I want to do the work for all accepted parameters. > ;-) Doesn't that make it an "accepted parameter"? Why not add it to the set? > Is this a correct way to do this, or is there a better way? I suppose you do this early in a function? Then at least choose a more specific exception (e. g. ValueError). If this is about commandline arguments -- argparse can handle such restrictions: $ cat demo.py import argparse parser = argparse.ArgumentParser() parser.add_argument("--check", choices=["pcpu", "rss"], default="all") print(parser.parse_args().check) $ python3 demo.py all $ python3 demo.py --check rss rss $ python3 demo.py --check ssr usage: demo.py [-h] [--check {pcpu,rss}] demo.py: error: argument --check: invalid choice: 'ssr' (choose from 'pcpu', 'rss')