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I would like to know how Python evaluates or expressions with integers. Research on the internet has not resulted in satisfactory answers.

Question 1

5<5 or 10

The above results in 10, which I do not understand why.

Question 2

How does :

False or 10 Return 10?

And:

How does :

True or 10 Return True?

Question 3

How does:

5 or 10 Return 5?

EDIT:

Rephrased question:

Why does Python return Boolean (True/False) when true and the Value (5 or 10) when false? I understand that it is a language, but is there a reason why it was mad so?

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  • 1
    Seems that the return of or is the first non False argument (or False if both arguments are False) Commented Jan 13, 2015 at 8:12
  • What do you mean how? Do you mean how is it implemented (in which case, in which distribution? CPython?) or do you really mean why (in which case: as opposed to what?) Commented Jan 13, 2015 at 8:17
  • Yes, Dmitry explains it correctly. Essentially, you just have to understand that the 'or' operator only cares about whether the objects evaluate to True and will return the first one that is, or simply the last one. In your examples of True or 10 and 5 or 10, both True and 5 evaluate to True (False and 0, for example, would be the counter-opposites in this case as both would evaluate to False). Also: The or operator evaluates the arguments in the order they're set in, but only if preceding ones fail; the second only gets evaluated if the first isn't True, and so on. Commented Jan 13, 2015 at 8:27
  • This one is a better duplicate: Boolean Python Value confusion Commented Jan 13, 2015 at 8:27

1 Answer 1

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or returns the first argument if it is True, otherwise the second argument. In Python, 0 and empty iterables like strings and lists are False, and everything else is True. So 5<5 or 10 evaluates to False or 10, so since the first argument is false it returns the second. In the other examples, the first argument is True, so that is returned.

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6 Comments

I think you are correct but the explanation is not as clear as it should be (at least for my taste).
Could you please check the rephrased question?
Sorry, your rephrased question doesn't make sense, because Python doesn't do that. As I said, it returns the first value, whatever it is, if it's true, otherwise the second value, whatever that is.
When we execute 0 or False, the output is False. But when we execute False or 0, the output is 0. This is what I meant in the rephrased question.
@WhiteFlameAB Please have a look at the question linked as duplicate. It is explained in detail there.
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