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Groups > comp.lang.python > #76512

Re: 'is not' or '!='

From Marko Rauhamaa <marko@pacujo.net>
Newsgroups comp.lang.python
Subject Re: 'is not' or '!='
Date 2014-08-18 23:53 +0300
Organization A noiseless patient Spider
Message-ID <87fvgt7c4i.fsf@elektro.pacujo.net> (permalink)
References <lsto1s$6gk$1@dont-email.me>

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"ElChino" <elchino@cnn.cn>:

> A newbie question to you; what is the difference between statements
> like:
>  if x is not None:
> and
> if x != None:

Do the following: take two $10 bills. Hold one bill in the left hand,
hold the other bill in the right hand.

Now, the bill in the left hand "is not" the bill in the right hand.
However, the bill in the left hand "==" the bill in the right hand.

> Without any context, which one should be preferred?
> IMHO, the latter is more readable.

In almost all cases, both tests would result in the same behavior.
However, the "is not" test is conceptually the correct one since you
want to know if x is the one and only None object. You don't want to be
fooled by an imposter object that simply looks like the None object.
Frankly, I don't know of any other object that is "==" to the None
object except None itself, but such objects could possible exist.


Marko

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Thread

'is not' or '!=' "ElChino" <elchino@cnn.cn> - 2014-08-18 22:35 +0200
  Re: 'is not' or '!=' MRAB <python@mrabarnett.plus.com> - 2014-08-18 21:53 +0100
  Re: 'is not' or '!=' Marko Rauhamaa <marko@pacujo.net> - 2014-08-18 23:53 +0300
    Re: 'is not' or '!=' "ElChino" <elchino@cnn.cn> - 2014-08-18 22:58 +0200
      Re: 'is not' or '!=' Ethan Furman <ethan@stoneleaf.us> - 2014-08-18 14:42 -0700
      Re: 'is not' or '!=' Ethan Furman <ethan@stoneleaf.us> - 2014-08-18 15:19 -0700
      Re: 'is not' or '!=' Chris Kaynor <ckaynor@zindagigames.com> - 2014-08-18 15:04 -0700
        Re: 'is not' or '!=' Thomas Rachel <nutznetz-0c1b6768-bfa9-48d5-a470-7603bd3aa915@spamschutz.glglgl.de> - 2014-08-19 11:49 +0200
      Re: 'is not' or '!=' Martin S <shieldfire@gmail.com> - 2014-08-19 14:42 +0200
      Re: 'is not' or '!=' Skip Montanaro <skip@pobox.com> - 2014-08-19 08:12 -0500
        Re: 'is not' or '!=' Marko Rauhamaa <marko@pacujo.net> - 2014-08-19 20:29 +0300
          Re: 'is not' or '!=' Tim Chase <python.list@tim.thechases.com> - 2014-08-19 12:34 -0500
            Re: 'is not' or '!=' Marko Rauhamaa <marko@pacujo.net> - 2014-08-19 21:18 +0300
          Re: 'is not' or '!=' Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-08-20 04:26 +1000
            Re: 'is not' or '!=' Marko Rauhamaa <marko@pacujo.net> - 2014-08-19 21:52 +0300
              Re: 'is not' or '!=' Marko Rauhamaa <marko@pacujo.net> - 2014-08-20 00:00 +0300
                Re: 'is not' or '!=' Ian Kelly <ian.g.kelly@gmail.com> - 2014-08-19 16:21 -0600
                Re: 'is not' or '!=' Marko Rauhamaa <marko@pacujo.net> - 2014-08-20 02:02 +0300
                Re: 'is not' or '!=' Rustom Mody <rustompmody@gmail.com> - 2014-08-20 22:03 -0700
                Re: 'is not' or '!=' Marko Rauhamaa <marko@pacujo.net> - 2014-08-21 08:56 +0300
            Re: 'is not' or '!=' Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-08-19 20:05 +0100
            Re: 'is not' or '!=' Terry Reedy <tjreedy@udel.edu> - 2014-08-19 18:23 -0400
      Re: 'is not' or '!=' Ian Kelly <ian.g.kelly@gmail.com> - 2014-08-19 10:42 -0600
        Re: 'is not' or '!=' Marko Rauhamaa <marko@pacujo.net> - 2014-08-19 20:36 +0300
      Re: 'is not' or '!=' Skip Montanaro <skip@pobox.com> - 2014-08-19 13:44 -0500
    Re: 'is not' or '!=' alister <alister.nospam.ware@ntlworld.com> - 2014-08-19 09:35 +0000
    Re: 'is not' or '!=' Thomas Rachel <nutznetz-0c1b6768-bfa9-48d5-a470-7603bd3aa915@spamschutz.glglgl.de> - 2014-08-19 11:53 +0200
  Re: 'is not' or '!=' Rustom Mody <rustompmody@gmail.com> - 2014-08-18 19:29 -0700
    Re: 'is not' or '!=' Steven D'Aprano <steve@pearwood.info> - 2014-08-19 08:36 +0000
      Re: 'is not' or '!=' Chris Angelico <rosuav@gmail.com> - 2014-08-19 18:47 +1000
      Re: 'is not' or '!=' Tim Chase <python.list@tim.thechases.com> - 2014-08-19 05:36 -0500
      Re: 'is not' or '!=' Ben Finney <ben+python@benfinney.id.au> - 2014-08-20 09:24 +1000
        Re: 'is not' or '!=' Rustom Mody <rustompmody@gmail.com> - 2014-08-19 21:01 -0700
          Re: 'is not' or '!=' Steven D'Aprano <steve@pearwood.info> - 2014-08-20 04:59 +0000
            Re: 'is not' or '!=' Rustom Mody <rustompmody@gmail.com> - 2014-08-19 22:25 -0700
              Re: 'is not' or '!=' Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-08-20 21:05 +1000
                Re: 'is not' or '!=' Chris Angelico <rosuav@gmail.com> - 2014-08-20 21:17 +1000
                Re: 'is not' or '!=' Thomas Rachel <nutznetz-0c1b6768-bfa9-48d5-a470-7603bd3aa915@spamschutz.glglgl.de> - 2014-08-21 20:31 +0200
                Re: 'is not' or '!=' Tim Chase <python.list@tim.thechases.com> - 2014-08-20 06:26 -0500
                Re: 'is not' or '!=' Chris Angelico <rosuav@gmail.com> - 2014-08-20 21:33 +1000
                Re: 'is not' or '!=' Robert Kern <robert.kern@gmail.com> - 2014-08-20 12:40 +0100
                Re: 'is not' or '!=' Rustom Mody <rustompmody@gmail.com> - 2014-08-20 05:01 -0700
  Re: 'is not' or '!=' Dan Stromberg <drsalists@gmail.com> - 2014-08-21 12:24 -0700
    Re: 'is not' or '!=' "ElChino" <elchino@cnn.cn> - 2014-08-21 21:42 +0200

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