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   James C :python: (jamescooke@fosstodon.org)'s status on Friday, 08-Nov-2024 08:28:35 JST James C :python:

   When is 0 not 0? When SymPy made it into an instance of its special Zero class of course! 😅

   *AND* you can't convert that to a Decimal by just casting it either 😬

   #Python

   • Embed this notice
     wizzwizz4 (wizzwizz4@fosstodon.org)'s status on Friday, 08-Nov-2024 08:28:31 JST wizzwizz4

     in reply to

     @jamescooke Showing the type was sufficient. After all:

     Python 3.9.2 (default, Feb 28 2021, 17:03:44)
     [GCC 10.2.1 20210110] on linux
     Type "help", "copyright", "credits" or "license()" for more information.
     >>> a = pow(2, 30, 1<<30)
     >>> type(a)
     <class 'int'>
     >>> a
     0
     >>> a is 0
     False

     `is`-equality is not a necessary condition for type-and-value equality, even for interned types like int and str.

   • Embed this notice
     James C :python: (jamescooke@fosstodon.org)'s status on Friday, 08-Nov-2024 08:28:32 JST James C :python:

     in reply to

     • wizzwizz4

     @wizzwizz4

     > You should not be writing code that relies on this behaviour in the first place.

     I'm not.

     That was just a screenshot of ipdb where I was debugging and surprised that an instance printed as "0" but wasn't the int 0.

     Happy to add a screenshot with a better way of demonstrating that the value I had in the dictionary was `sp.S.Zero` and not `int(0)`, even though they `== 0` as `True` - what _should_ I have done?

     alcinnz repeated this.
   • Embed this notice
     James C :python: (jamescooke@fosstodon.org)'s status on Friday, 08-Nov-2024 08:28:33 JST James C :python:

     in reply to

     • wizzwizz4

     @wizzwizz4 Testing zero with `is` is safe because it's got a fixed memory address: https://realpython.com/python-is-identity-vs-equality/#when-only-some-integers-are-interned

     Try your code with 256 and 257 - you'll see that 256 gives True and 257 gives False.

   • Embed this notice
     wizzwizz4 (wizzwizz4@fosstodon.org)'s status on Friday, 08-Nov-2024 08:28:33 JST wizzwizz4

     in reply to

     @jamescooke It's not safe: that's an undocumented CPython implementation detail, and could change at any time. (Compare Java, where the equivalent behaviour is part of the language specification.) CPython is not the only implementation of Python.

     You should not be writing code that relies on this behaviour in the first place. The decimal.Decimal limitation is a valid thing to be annoyed about (though it is documented), but is not working is not.

     >>> 7832 is 7832
     True

   • Embed this notice
     wizzwizz4 (wizzwizz4@fosstodon.org)'s status on Friday, 08-Nov-2024 08:28:34 JST wizzwizz4

     in reply to

     @jamescooke When is 7832 not 7832?

     >>> x = 7832
     >>> y = 7832
     >>> x is y
     False

     You're holding is wrong.