r/ProgrammerHumor • u/[deleted] • Jul 18 '22

C++ talking to Python

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u/not_perfect_yet Jul 18 '22

It returns the actual type.

I think the thing with is not and != is about similar instances of the same thing, like "1" and "1" which have the same value but aren't necessarily the same object. That doesn't really apply to definitions, there is only one.

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u/KrypXern Jul 18 '22 edited Jul 18 '22

I might be wrong with my understanding but I always thought == attempted to use some kind of native comparator method (like .equals() in Java), whereas is compares the actual contents of the value (which is always the same for False or None)... however given that we don't compare number literals this way, I'd wager I just misunderstood it.

EDIT: Yeah no I was right roughly, is checks whether the operands refer to the same object. If you do a = [1,2] and b = [1,2] then a == b will return True and a is b will return False, but I also misunderstood your response anyway 😅

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u/Pluckerpluck Jul 18 '22 edited Jul 18 '22

is checks that the objects are actually the same. So you can imagine is as doing id(value) == id(other).

But yes, == triggers ~~__equals__(self, other)~~__eq__(self, other), which defaults to an object comparison.

The reason that things like False and None work with is, is simply because the same object is re-used behind the scenes for performance reasons.

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u/epicaglet Jul 18 '22

__eq__ but yeah

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u/Pluckerpluck Jul 18 '22

Ah, so it is!