Path: csiph.com!fu-berlin.de!uni-berlin.de!not-for-mail From: Peter Otten <__peter__@web.de> Newsgroups: comp.lang.python Subject: 0 equals False, was Re: (unknown) Date: Wed, 23 Mar 2016 09:51:34 +0100 Organization: None Lines: 51 Message-ID: References: Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7Bit X-Trace: news.uni-berlin.de EVk7Q2KLzTQ6yBlpl2Xzlwr9RBvHJbrultRRnlj1X68Q== 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; 'operator': 0.03; 'true,': 0.04; 'context': 0.05; 'false,': 0.07; 'feature.': 0.07; 'behavior,': 0.09; 'bool': 0.09; 'discriminate': 0.09; 'item,': 0.09; 'overwrite': 0.09; 'received:80.91': 0.09; 'received:80.91.229': 0.09; 'received:gmane.org': 0.09; 'received:list': 0.09; 'bug': 0.10; 'python': 0.10; "'a',": 0.16; '(meaning': 0.16; '0.0,': 0.16; 'dictionaries': 0.16; 'different?': 0.16; 'false:': 0.16; 'fits': 0.16; 'keys.': 0.16; 'nick': 0.16; 'pythonic': 0.16; 'received:80.91.229.3': 0.16; 'received:dip0.t-ipconnect.de': 0.16; 'received:io': 0.16; 'received:plane.gmane.org': 0.16; 'received:psf.io': 0.16; 'received:t-ipconnect.de': 0.16; '{true:': 0.16; 'wrote:': 0.16; 'case.': 0.18; 'odd': 0.18; 'all,': 0.20; 'versions': 0.20; 'arguments': 0.22; 'header:User-Agent:1': 0.26; '(which': 0.26; 'header:X-Complaints-To:1': 0.26; 'compatible': 0.27; 'function': 0.28; 'accepts': 0.29; 'dictionary': 0.29; 'hash': 0.29; "i'm": 0.30; 'certainly': 0.30; "i'd": 0.31; 'true.': 0.33; 'advice': 0.35; 'clear': 0.35; 'false': 0.35; 'identity': 0.35; 'item': 0.35; 'but': 0.36; '(i.e.': 0.36; 'to:addr:python-list': 0.36; 'received:org': 0.37; 'desired': 0.37; 'why': 0.39; 'sure': 0.39; "didn't": 0.39; 'easily': 0.39; 'to:addr:python.org': 0.40; 'received:de': 0.40; 'some': 0.40; 'your': 0.60; 'behavior': 0.61; 'provide': 0.61; 'today,': 0.62; 'different': 0.63; 'between': 0.65; 'banging': 0.84 X-Injected-Via-Gmane: http://gmane.org/ X-Gmane-NNTP-Posting-Host: p57bd95b9.dip0.t-ipconnect.de User-Agent: KNode/4.13.3 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:105527 Nick Eubank wrote: > Hello All, > > > Found an odd behavior I'd never known about today, not sure if it's a bug > or known. Python 3.4.4 (anaconda). This is a feature. Old versions of Python did not have True and False, so they were added in a compatible way. > True, False, 0, 1 can all be used as dictionary keys. > > But Apparently True and 1 hash to the same item and False and 0 hash to > the same item, so they can easily overwrite (which I spent a while banging > my head over today). > > In other words: > > In[1]: > d = {True: 'a', False: 'b'} > d[0] = 'z' > d[False] > > Out[1]: > 'z' > > I understand that True and False are sub-types of ints, but it's not clear > to me why (i.e. certainly didn't feel intuitive) that they would be > treated the same as keys. > > Relatedly, if this is a desired behavior, any advice one how best to work > with dictionaries when one wants "True" and 1 to be different? I'm working > on a function that accepts arguments that may be "True" or 1 (meaning very > different things) and am seeking a pythonic solution... The pythonic solution is "don't do this". The == operator cannot discriminate between 0, 0.0, and False, or 1, 1.0, and True. True and False are singletons, so you can check identity with x is True or x is False A type check will also work: type(x) == bool isinstance(x, bool) # bool cannot be subclassed If you provide some context we may be able to come up with an alternative approach that fits your use case.