Does Python have the Elvis operator?

Question

The ternary operator in many languages works like so:

x = f() ? f() : g()

Where if f() is truthy then x is assigned the value of f(), otherwise it is assigned the value of g(). However, some languages have a more succinct elvis operator that is functionally equivalent:

x = f() ?: g()

In python, the ternary operator is expressed like so:

x = f() if f() else g()

But does python have the more succinct elvis operator?

Maybe something like:

x = f() else g() # Not actually valid python

Undoing the dupe-close because this is *not* asking for null-coalescing behavior. (Also, the accepted answer on the old dupe target is bug-prone and terrible.) — user2357112 supports Monica, Dec 13 '18 at 00:08

score 36 · Accepted Answer · edited Jan 17 '20 at 01:42

36

Yes

Python does have the elvis operator. It is the conditional or operator:

x = f() or g()

f() is evaluated. If truthy, then x is assigned the value of f(), else x is assigned the value of g().

Reference: https://en.wikipedia.org/wiki/Elvis_operator#Analogous_use_of_the_short-circuiting_OR_operator

edited Jan 17 '20 at 01:42

Jerry Jeremiah

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answered Feb 15 '18 at 17:32

Robᵩ

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YES I could not find anywhere that "elvis operator" was mentioned, but this is functionally equivalent. Thank you. – Cory Klein Feb 15 '18 at 17:33
And I've never heard of "elvis operator" before. – Robᵩ Feb 15 '18 at 17:34
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If you interpret `?:` as a smiley, the curl of the question mark resembles Elvis' emblematic hairstyle. – FeepingCreature Nov 29 '18 at 08:34

Aleksandr Dubinsky · Answer 2 · 2020-12-27T17:34:14.423

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NB Python does not have the null-coalescing operator defined by:

a if a is not None else b

The or operator in a or b checks the truthiness of a which is False when a==0 or len(a)==0 or other similar situations. See What is Truthy and Falsy

There is a proposal to add such operators PEP 505

edited Dec 27 '20 at 17:34

answered Dec 27 '20 at 16:38

Aleksandr Dubinsky

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OP specifically asked about checking `a` for truthiness, not checking `a is not None`. – CrazyChucky Dec 27 '20 at 16:50
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@CrazyChucky Hmm, I may have fudged the distinction between the elvis operator and the null-coalescing operator. Nevertheless I'll leave this answer up for others who may have the same confusion. – Aleksandr Dubinsky Dec 27 '20 at 17:23
Good point, I think it's worth pointing out. Perhaps mention specifically that the Elvis and null-coalescing operator are similar, but have this distinction? – CrazyChucky Dec 27 '20 at 17:25
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@CrazyChucky Edited. I'll point out that some languages, like Kotlin, use `?:` for null-coallescing and Wikipedia actually has sections for both behaviors under ["elvis operator"](https://en.wikipedia.org/wiki/Elvis_operator#Object_reference_variant) and in examples has entries for '??' as well. So the term is not exactly clear-cut. – Aleksandr Dubinsky Dec 27 '20 at 17:36

score -3 · Answer 3 · answered Mar 11 '20 at 05:48

-3

>>> a = [1,2,3]
>>> b = [4,5,6]
>>> c = [4]
>>> a + (b,c)[b>c]
[1, 2, 3, 4]
>>> a + (b,c)[b<c]
[1, 2, 3, 4, 5, 6]
>>>

Python elvis operation is

(testIsFalse, testIsTrue)[test]

The Java equivalent is

test ? testIsTrue:testIsFalse

answered Mar 11 '20 at 05:48

Blessed Geek

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That's not what the elvis operator does. You're thinking of the ternary operator. – Aleksandr Dubinsky Dec 27 '20 at 16:34

Does Python have the Elvis operator?

3 Answers3

Yes

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