Path: csiph.com!news.swapon.de!fu-berlin.de!uni-berlin.de!not-for-mail From: Ian Kelly Newsgroups: comp.lang.python Subject: Re: Question about code writing '% i, callback' Date: Mon, 30 Nov 2015 11:01:55 -0600 Lines: 48 Message-ID: References: <25af8ac3-5fc7-44bd-a73f-7a870b69515a@googlegroups.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 X-Trace: news.uni-berlin.de M+ishJQYB7/ORtFmIoEmqgpdZyEVOfVj2Uiau2O/CLjQ== 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; 'received:209.85.223': 0.03; 'subject:Question': 0.05; 'method,': 0.07; 'subject:code': 0.07; 'callback': 0.09; 'posted.': 0.09; 'def': 0.13; 'argument': 0.15; 'above?': 0.16; 'callback)': 0.16; 'formatting.': 0.16; 'parameter,': 0.16; 'printf-style': 0.16; 'received:io': 0.16; 'received:psf.io': 0.16; 'subject:writing': 0.16; 'wrote:': 0.16; 'string': 0.17; '2015': 0.20; '%s"': 0.22; 'arguments': 0.22; 'explicit': 0.22; 'parameter': 0.22; 'trying': 0.22; 'am,': 0.23; 'defined': 0.23; 'second': 0.24; 'recognized': 0.24; 'header:In- Reply-To:1': 0.24; 'mon,': 0.24; 'example': 0.26; 'parameters': 0.27; 'message-id:@mail.gmail.com': 0.27; 'function': 0.28; 'looks': 0.29; '(it': 0.29; 'implicitly': 0.29; 'thus,': 0.29; 'print': 0.30; 'code': 0.30; 'class.': 0.30; 'skip:_ 10': 0.32; 'related': 0.32; 'run': 0.33; 'class': 0.33; 'definition': 0.34; 'me?': 0.34; 'received:google.com': 0.35; 'could': 0.35; 'false': 0.35; 'instance': 0.35; 'nov': 0.35; 'but': 0.36; 'received:209.85': 0.36; 'to:addr:python-list': 0.36; 'subject:: ': 0.37; 'two': 0.37; 'being': 0.37; 'method': 0.37; 'received:209': 0.38; 'button': 0.38; 'takes': 0.39; 'to:addr:python.org': 0.40; 'skip:u 10': 0.61; '30,': 0.63; 'above,': 0.63; 'strange': 0.63; 'to:name:python': 0.84 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 :content-type; bh=lZ11fujKwyG29do8wdfiMSrDTooOBC80/TQN5ligPdM=; b=wVWtpvtYJEg41aifoGhrxwKlmHlQiWkSIME+yZRx5EnAcMX2ueLNiL8lIF+vlEQgRS gUn6qwCP87jENKo7p/z+PkBTmwdUUSPIU97Zw6K8OXwUSOsS++3rqCRcS5xBolGSViqA xkHkjMy+wUSsH6x3J9RRAkoBjUVaGKtR9rTcPsh+00Bb/TOUheOMEDCJzMHTblFr88/g Elvf3H2YMlJ+C1GrMHgFwFmz8qsg/Fbkg2p9wzLrFu2LCwsgpIOU6KHFoev1VDpo2skJ VmgBENFlFG/Q51w9JUJsikz5Rft9rO4GzdYgRRdKt0y9+9JuDWgoCBgkmqBuC+zfCgnf NOKQ== X-Received: by 10.107.137.226 with SMTP id t95mr57421735ioi.188.1448902954718; Mon, 30 Nov 2015 09:02:34 -0800 (PST) In-Reply-To: <25af8ac3-5fc7-44bd-a73f-7a870b69515a@googlegroups.com> 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:99745 On Mon, Nov 30, 2015 at 10:44 AM, fl wrote: > I come across the following code snippet. > > for i in range(10): > def callback(): > print "clicked button", i > UI.Button("button %s" % i, callback) > > The content inside parenthesis in last line is strange to me. > > "button %s" % i, callback These are the arguments being passed to UI.Button. The first argument is: "button %s" % i This is an example of printf-style string formatting. See the link that Zachary posted. The second argument is the function named callback. > That is, the writing looks like recognized as three items when I try with a > class definition (it can run with this): > > class buibutton(): > print 'sd' > def __nonzero__(self): > return False > > def Button(str, ii, callbackk): > > return > > > Could you explain it to me? How is this related to the example above? Here, Button is defined as a method of a class. Since it's a method, the first parameter is the "self" parameter, which will implicitly take the value of the class instance that you're calling the Button method on. If you're trying to call this like above, then the second parameter "ii" will take the value of the string from the example above, and callbackk will take the value of the callback argument from above. Thus, the method that you've defined has three parameters but only takes two explicit arguments.