Number is int returning False

Question

When I do this:

>>> 1 is int
False

It returns False, even when I would expect it to return True. The same behavior occurs when attempting to type-check a variable.

>>> a = 1
>>> a is int
False

I understand that this has something to do with using is instead of isinstance or type.

>>> type(1)
<class 'int'>
>>> isinstance(1, int)
True
>>> type(1) is int
True

Could someone explain exactly why using is does not work in this case? It makes sense to me semantically that it would return True instead of False.

You should probably read on the `is` operator. It certainly doesn't do what you believe it does. — Vincent Savard, Apr 27 '17 at 17:33
This question is really about that classes are first-class objects in Python, not a question regarding the `is` operator per se, imo. — , Apr 27 '17 at 17:35
@Tobias Not sure, I believe OP is reading the statement `1 is int` as "1 is an integer", which demonstrates a misconception of what `is` does. — Vincent Savard, Apr 27 '17 at 17:37
@Tobias it's about huge misunderstanding about what `is` is for. — vaultah, Apr 27 '17 at 17:37
Wrote up an answer but couldn't post it. Make sure not to confuse **is an** with **is**. — Apollys supports Monica, Apr 27 '17 at 17:38
My issue is that it makes sense *semantically* for `1 is int` to be `True`, yet it isn't. — Remolten, Apr 27 '17 at 17:43
@Remolten It doesn't make sense, that's why you've been told to read on what `is` does. — Vincent Savard, Apr 27 '17 at 17:47
@Apollys I don't see why `is` shouldn't default to the equivalent of `is an` in this case. There's certainly no reason it couldn't be interpreted correctly, though it would cause the `is` operator to have differing usages based on context. — Remolten, Apr 27 '17 at 17:55
... which is a very, very good reason not to interpret it as you want. — Vincent Savard, Apr 27 '17 at 17:56
No, semantically, "1 is int" is nonsense. It's like saying "Skippy is dog." If you said "Skippy is a dog" that makes sense and is true. In this sense, python is actually in direct agreement with English grammar. — Apollys supports Monica, Apr 27 '17 at 17:59
@Apollys Good point. Perhaps Python should introduce `is a` and `is an`. — Remolten, Apr 27 '17 at 18:00

score 3 · Accepted Answer · edited Apr 27 '17 at 17:45

3

1 is an int, int is a type.

They can't be equal or be the same object, so is is always False between those two (is checks if the objects are actually the same object).

So this is a question of misinterpreting what is checks. The correct way indeed is to use isinstance like you did.

edited Apr 27 '17 at 17:45

user2357112

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answered Apr 27 '17 at 17:33

Jean-François Fabre

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Understood. My issue is that it makes sense *semantically* for `1 is int` to be `True`, yet it isn't. – Remolten Apr 27 '17 at 17:42
yes, natural language vs python ;) same issue with the classical: `if a == 1 or 2:` that we see each week – Jean-François Fabre Apr 27 '17 at 17:46
1

@Remolten: It makes sense with the semantics of the English word "is", but not with the semantics of the Python operator `is`. – user2357112 Apr 27 '17 at 17:46
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@Jean-FrançoisFabre: `==` doesn't start with a reference comparison (that's the final fallback), and it doesn't involve a type comparison. You can have stuff like `x = float('nan'); x != x`, where the same object compares unequal to itself, or `1 == 1.0`, where objects of different type compare equal. – user2357112 Apr 27 '17 at 17:54
@user2357112 totally! you're right. I'll delete my comment. but how can references be equal (final fallback) if the values are different? damn the `x = float('nan')` example is good!! – Jean-François Fabre Apr 27 '17 at 17:58

Number is int returning False

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