Python: What is the `is` function?

Question

This might be a stupid question, but what exactly is the is function, and when would one use it?

From the context, i guess i could infer that it's equivalent to ==; but if that's the case, why have both? The Built-in Functions Reference shows nothing, and help(is) returns a SyntaxError.

No, because you could have two objects with the same values, but they wouldn't be the *same* objects. Suppose you and I live in the same apartment complex. Our apartments might be absolutely identical in every way (`my_apartment == your_apartment`), but they're two different places (`my_apartment is not your_apartment`). — Kirk Strauser, Jun 30 '13 at 19:15

score 3 · Accepted Answer · answered Jun 30 '13 at 19:02

3

is checks if the objects have the same identity. == only checks if they are equal.

>>> L1 = [1,2,3]
>>> L2 = [1,2,3]
>>> L1 is L2
False
>>> L1 == L2
True

answered Jun 30 '13 at 19:02

michaelmeyer

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Do you know where the is reference on this? I take it it's not in Built-in Functions. – Noob Saibot Jun 30 '13 at 19:04
In other words, `L1 is L2` <=> `id(L1) == id(L2)` – Asad Saeeduddin Jun 30 '13 at 19:04
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Also note that according to PEP 8, you should use `is` when comparing to `None`. – Maxime Chéramy Jun 30 '13 at 19:05
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@NoobSaibot: type `help("is")` in a prompt. – michaelmeyer Jun 30 '13 at 19:06
@Maxime: That's the ambiguity that led me to ask the question in the first place, thanks! – Noob Saibot Jun 30 '13 at 19:17

Python: What is the `is` function?

1 Answers1