Path: csiph.com!v102.xanadu-bbs.net!xanadu-bbs.net!goblin2!goblin.stu.neva.ru!newsfeed.xs4all.nl!newsfeed2a.news.xs4all.nl!xs4all!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 0.003 X-Spam-Evidence: '*H*': 0.99; '*S*': 0.00; 'python,': 0.02; 'else:': 0.03; '(at': 0.04; 'string': 0.09; 'raises': 0.09; 'received:209.85.219': 0.09; 'subject:None': 0.09; 'subject:string': 0.09; 'cc:addr:python-list': 0.11; 'python': 0.11; 'assume': 0.14; 'containers': 0.16; 'iterable:': 0.16; 'roy': 0.16; 'tuple,': 0.16; 'typeerror:': 0.16; 'which,': 0.16; 'bit': 0.19; 'seems': 0.21; '>>>': 0.22; 'cc:addr:python.org': 0.22; '>>>': 0.24; 'documented': 0.24; 'cc:2**0': 0.24; 'least': 0.26; 'header:In-Reply-To:1': 0.27; 'needed.': 0.30; 'restrict': 0.30; 'message-id:@mail.gmail.com': 0.30; 'that.': 0.31; 'comparison': 0.31; 'url:python': 0.33; 'totally': 0.33; 'noticed': 0.34; 'sense': 0.34; 'received:209.85': 0.35; 'equal': 0.35; 'but': 0.35; 'received:google.com': 0.35; 'false': 0.36; 'subject:?': 0.36; 'url:org': 0.36; 'received:209': 0.37; 'skip:& 10': 0.38; 'list,': 0.38; 'that,': 0.38; 'little': 0.38; 'according': 0.40; 'url:3': 0.61; 'here:': 0.62; 'charset:iso-2022-jp': 0.65; 'smith': 0.68; 'default': 0.69; 'url:me': 0.69; "'foo'": 0.84; 'skip:\x1b 30': 0.84; 'url:reference': 0.84; 'str.': 0.91; 'hand,': 0.93 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:date :message-id:subject:from:to:cc:content-type; bh=h5rDRNa086XRtj41N5aeyhux4Pp58lKTMP1cyc+QT+E=; b=m69JD1yb+8vtx6BMNNQxnouBICRBVnY2vj2xJZ9udRoIFGJ6OytFJY0wLotKAz5gRo eKuBgbGDwuMoj8tD3/zx9XUMOkhfR30OibJl54n2BOXDc8jx57AH4dMZ5oyPTgp2bFel z6ED++zMCILHSzj2q2WxUFsI6zPiA5+9242dNZVGWHHg051aMeEcwUAYfRo7Em7rdxNR Qj8mPiEMZPt0FbrqzbITqgOm7G6TZZY2KvJ9prlRX+oiBP9DV27kZDYvDgnrcAJWgHGz uRGsZfS8OBpJ1u8XBVDKWAk1SV3WrbVx56mtVya5bF7YEJePHRbm3KJBMBCRnrpL32AR m6DQ== X-Gm-Message-State: ALoCoQlWhzWxp3BeqiHEk83iK5jRaND5Mi4a9/GPhy6MAPRG/+vNzNLVisQK6PTXsFSEVS98W2XM MIME-Version: 1.0 X-Received: by 10.60.94.75 with SMTP id da11mr26908887oeb.43.1402330429084; Mon, 09 Jun 2014 09:13:49 -0700 (PDT) X-Originating-IP: [143.89.76.162] In-Reply-To: <048960da-c132-407f-b1b3-4612a3dd7697@googlegroups.com> References: <048960da-c132-407f-b1b3-4612a3dd7697@googlegroups.com> Date: Tue, 10 Jun 2014 00:13:49 +0800 Subject: Re: None in string => TypeError? From: Shiyao Ma To: Roy Smith Content-Type: multipart/alternative; boundary=089e011603f4169c9d04fb697f86 Cc: Python X-BeenThere: python-list@python.org X-Mailman-Version: 2.1.15 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: 82 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1402330438 news.xs4all.nl 2960 [2001:888:2000:d::a6]:51262 X-Complaints-To: abuse@xs4all.nl Xref: csiph.com comp.lang.python:73046 --089e011603f4169c9d04fb697f86 Content-Type: text/plain; charset=ISO-2022-JP Content-Transfer-Encoding: 7bit 2014-06-09 23:34 GMT+08:00 Roy Smith : > We noticed recently that: > > >>> None in 'foo' > > raises (at least in Python 2.7) > > TypeError: 'in ' requires string as left operand, not NoneType > > This is surprising. The description of the 'in' operatator is, 'True if > an item of s is equal to x, else False '. From that, I would assume it > behaves as if it were written: > > for item in iterable: > if item == x: > return True > else: > return False > > why the extra type check for str.__contains__()? That seems very > unpythonic. Duck typing, and all that. > It's a little bit inconsistent. But it's clearly documented here: https://docs.python.org/3/reference/expressions.html#in Which, according to its own logic, the string is not a *container* type. It's just some chars, and that totally makes sense for to restrict the type of x in "str" to be convertible to type str. On the other hand, containers like list, and tuple, they are heterogeneous by default in Python, so a item by item comparison is needed. -- 吾輩は猫である。ホームーページはhttp://introo.me。 --089e011603f4169c9d04fb697f86 Content-Type: text/html; charset=ISO-2022-JP Content-Transfer-Encoding: base64 PGRpdiBkaXI9Imx0ciI+PGRpdiBjbGFzcz0iZ21haWxfZXh0cmEiPjxkaXYgY2xhc3M9ImdtYWls X3F1b3RlIj4yMDE0LTA2LTA5IDIzOjM0IEdNVCswODowMCBSb3kgU21pdGggPHNwYW4gZGlyPSJs dHIiPiZsdDs8YSBocmVmPSJtYWlsdG86cm95QHBhbml4LmNvbSIgdGFyZ2V0PSJfYmxhbmsiPnJv eUBwYW5peC5jb208L2E+Jmd0Ozwvc3Bhbj46PGJyPjxibG9ja3F1b3RlIGNsYXNzPSJnbWFpbF9x dW90ZSIgc3R5bGU9Im1hcmdpbjowcHggMHB4IDBweCAwLjhleDtib3JkZXItbGVmdDoxcHggc29s aWQgcmdiKDIwNCwyMDQsMjA0KTtwYWRkaW5nLWxlZnQ6MWV4Ij4NCldlIG5vdGljZWQgcmVjZW50 bHkgdGhhdDo8YnI+DQo8YnI+DQomZ3Q7Jmd0OyZndDsgTm9uZSBpbiAmIzM5O2ZvbyYjMzk7PGJy Pg0KPGJyPg0KcmFpc2VzIChhdCBsZWFzdCBpbiBQeXRob24gMi43KTxicj4NCjxicj4NClR5cGVF cnJvcjogJiMzOTtpbiAmbHQ7c3RyaW5nJmd0OyYjMzk7IHJlcXVpcmVzIHN0cmluZyBhcyBsZWZ0 IG9wZXJhbmQsIG5vdCBOb25lVHlwZTxicj4NCjxicj4NClRoaXMgaXMgc3VycHJpc2luZy4gJm5i c3A7VGhlIGRlc2NyaXB0aW9uIG9mIHRoZSAmIzM5O2luJiMzOTsgb3BlcmF0YXRvciBpcywgJiMz OTtUcnVlIGlmIGFuIGl0ZW0gb2YgcyBpcyBlcXVhbCB0byB4LCBlbHNlIEZhbHNlICYjMzk7LiAm bmJzcDtGcm9tIHRoYXQsIEkgd291bGQgYXNzdW1lIGl0IGJlaGF2ZXMgYXMgaWYgaXQgd2VyZSB3 cml0dGVuOjxicj4NCjxicj4NCmZvciBpdGVtIGluIGl0ZXJhYmxlOjxicj4NCiZuYnNwOyAmbmJz cDsgaWYgaXRlbSA9PSB4Ojxicj4NCiZuYnNwOyAmbmJzcDsgJm5ic3A7ICZuYnNwOyByZXR1cm4g VHJ1ZTxicj4NCmVsc2U6PGJyPg0KJm5ic3A7ICZuYnNwOyByZXR1cm4gRmFsc2U8YnI+DQo8YnI+ DQp3aHkgdGhlIGV4dHJhIHR5cGUgY2hlY2sgZm9yIHN0ci5fX2NvbnRhaW5zX18oKT8gJm5ic3A7 VGhhdCBzZWVtcyB2ZXJ5IHVucHl0aG9uaWMuICZuYnNwO0R1Y2sgdHlwaW5nLCBhbmQgYWxsIHRo YXQuPHNwYW4gY2xhc3M9IiI+PGZvbnQgY29sb3I9IiM4ODg4ODgiPjxicj48L2ZvbnQ+PC9zcGFu PjwvYmxvY2txdW90ZT48ZGl2Pjxicj48L2Rpdj48ZGl2Pkl0JiMzOTtzIGEgbGl0dGxlIGJpdCBp bmNvbnNpc3RlbnQuJm5ic3A7IEJ1dCBpdCYjMzk7cyBjbGVhcmx5IGRvY3VtZW50ZWQgaGVyZTog PGEgaHJlZj0iaHR0cHM6Ly9kb2NzLnB5dGhvbi5vcmcvMy9yZWZlcmVuY2UvZXhwcmVzc2lvbnMu aHRtbCNpbiI+aHR0cHM6Ly9kb2NzLnB5dGhvbi5vcmcvMy9yZWZlcmVuY2UvZXhwcmVzc2lvbnMu aHRtbCNpbjwvYT48YnI+DQo8YnI+PC9kaXY+PGRpdj5XaGljaCwgYWNjb3JkaW5nIHRvIGl0cyBv d24gbG9naWMsIHRoZSBzdHJpbmcgaXMgbm90Jm5ic3A7IGEgKmNvbnRhaW5lciogdHlwZS4gSXQm IzM5O3MganVzdCBzb21lIGNoYXJzLCBhbmQgdGhhdCB0b3RhbGx5IG1ha2VzIHNlbnNlIGZvciB0 byByZXN0cmljdCB0aGUgdHlwZSBvZiB4IGluICZxdW90O3N0ciZxdW90OyB0byBiZSBjb252ZXJ0 aWJsZSB0byB0eXBlIHN0ci4gT24gdGhlIG90aGVyIGhhbmQsIGNvbnRhaW5lcnMgbGlrZSBsaXN0 LCBhbmQgdHVwbGUsIHRoZXkgYXJlIGhldGVyb2dlbmVvdXMgYnkgZGVmYXVsdCBpbiBQeXRob24s IHNvIGEgaXRlbSBieSBpdGVtIGNvbXBhcmlzb24gaXMgbmVlZGVkLjxicj4NCjwvZGl2PjwvZGl2 Pjxicj48YnIgY2xlYXI9ImFsbCI+PGJyPi0tIDxicj48ZGl2IGRpcj0ibHRyIj48ZGl2Pjxicj48 L2Rpdj48ZGl2PhskQjhjR1okT0ctJEckIiRrISMlWyE8JWAhPCVaITwlOCRPGyhCPGEgaHJlZj0i aHR0cDovL2ludHJvby5tZSIgdGFyZ2V0PSJfYmxhbmsiPmh0dHA6Ly9pbnRyb28ubWU8L2E+GyRC ISMbKEI8YnI+PC9kaXY+PC9kaXY+DQo8L2Rpdj48L2Rpdj4NCg== --089e011603f4169c9d04fb697f86--