an irregular anomaly in python tuple

Question

i create two identical tuples and use is operator on them the answer that should come is false but when i use it in vscode/atom/notepadd++ it comes true but when i use the same code in pthon run through cmd it comes false

a = (1,2,3)
b = (1,2,3)

print(a is b)

actual result should be false and it is false when i use python through cmd or some online python compiler but when i used vscode to write the above code and create a .py file it comes true. The following picture shows what i am trying to say.

My code in vscode and executed through terminal and directly in terminal:

CPython does not promise to intern immutatble objects (strings/tuple) by default, but in practice, a lot of places in the Python codebase do reuse already-created objects. This is the reason if you check id for such small objects is same. — Mahesh Karia, Jan 07 '19 at 09:07
Which Python is being used by the IDE? Are you using the same one yourself? Since a tuple of integers is a completely immutable, I could see other versions of Python interning the object, resulting in them having the same id. I don't expect this out of CPython though--it would have been helpful to see the rest of the version string in the picture you took. — John Szakmeister, Jan 07 '19 at 09:10
As an example, PyPy will intern the tuple, at least if run against the script rather than interactively. — John Szakmeister, Jan 07 '19 at 09:12
i am using python 3.7. and when code is written in ide but executed using a terminal — Shehryar khan, Jan 07 '19 at 11:00
It looks like this is a new feature of Python 3.7 as a result of [some work](https://github.com/python/cpython/commit/7ea143ae795a9fd57eaccf490d316bdc13ee9065) on the AST-level constant folding (because a tuple of numbers is really just a constant) and [some work](https://github.com/python/cpython/commit/87010e85cb37192d63b1a30e5fabba307ad5a3f5) on the peephole optimizer. — John Szakmeister, Jan 07 '19 at 12:46
so if anyone can tell me whats happening and what should i do. because i am learning python and now i am stuck at this — Shehryar khan, Jan 07 '19 at 14:51
What is happening is that Python 3.7 now treats `(1, 2, 3)` as a constant and is, in effect, interning the result when running as a script (it's sharing the same value in the compiled version of the file). It is safe for Python to do this because tuples and integers are both immutable, which means tuples of integers are also immutable and safe to share--just like what Python does for strings. Why is this a problem for you? If the material for the class requires the ids to not be the same, then you'll need to fall back to the latest in the Python 3.6. 3.6 will produce different ids still. — John Szakmeister, Jan 07 '19 at 16:02

score 0 · Answer 1 · answered Jan 07 '19 at 09:36

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I checked it in linux terminal result is False. It is because a is b will become True when a and b are pointing to same object. is does not compare values of the tuples. If you define b=a then you will get True. You can check this discussion Python "is" statement: what is happening?

answered Jan 07 '19 at 09:36

user10340258

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That's not what is happening here--two separate tuples are being created. The OP is expecting the ids to be different, but in one circumstance they are not. – John Szakmeister Jan 07 '19 at 09:40
I checked it in both ways, in python terminal and running code written in a notepad.. Result is always false. – user10340258 Jan 07 '19 at 09:50
That means we're possibly missing a piece of information, not that he assigned `a` to `b`. For instance, using pypy you can get this result. PyPy can intern tuples of integers because everything is immutable, just like CPython does for strings. :-) – John Szakmeister Jan 07 '19 at 09:55
user10340258 did you used a tuple. i used python 3.7 – Shehryar khan Jan 07 '19 at 10:59
I just wrote 3 lines as written by you and used python 2.7.13. – user10340258 Jan 07 '19 at 11:09
i am using python 3.7 if you can kindly use that and tell me whats happening that would be great – Shehryar khan Jan 07 '19 at 14:48
@Shehryarkhan sorry, I can't upgrade python now as several other codes are running. – user10340258 Jan 08 '19 at 03:31

score 0 · Answer 2 · answered Jan 07 '19 at 17:12

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This a change introduced in Python 3.7.0 alpha 4 by change bpo-29469: Move constant folding from bytecode layer to AST layer.

We see different behavior between the command line (REPL) and a script. Each line entered at the command line is compiled and executed when entered. All of a script is compiled at once.

In general, for ordinary comparisons, you should use the equality operator (==) instead of the identity operator (is). For all objects the equality operator has a variety of strategies for completing the comparison (actually each class can provide its own __eq__ operator). The identity operator will only compare the objects' ids.

answered Jan 07 '19 at 17:12

Doug Henderson

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To confirm this behavior for any python version, at the python interactive prompt, enter `a=(1,2,3); b=(1,2,3); print(a is b)` on one line. – Doug Henderson Jan 07 '19 at 22:35
wow i mean ur amazing thank u so much for your help i was just stuck at another thing just like this and you saved my time. Just one thing normally the whole script is compiled at once and command line is used for teaching purpose. which one is correct thing to do command line or the entire script?? – Shehryar khan Jan 13 '19 at 17:58
so @Doug Henderson each line in idle this >>> mean this is gonna be 1 script and the next >>> will be another script – Shehryar khan Jan 15 '19 at 00:56

an irregular anomaly in python tuple

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