Is There '?' Control Flow in Python?

Question

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Python Ternary Operator

Is there control flow operator similar to '?' of C/C++ in python?

If there is a chunk of code similar to this:

return n <= 1 ? n : fibo(n-1) + fibo(n-2)

Will got an error like this:

File "fibonacci.py", line 2
    return n <= 1 ? n : fibo(n-1) + fibo(n-2)
                  ^
SyntaxError: invalid syntax

It may be called that incorrectly; It takes three operands and so it is ternary in the same way that addition is binary. It happens that there arent many ternary operators in python or other algol descendands. This is uniquely identified as in phihag's answer as a "Conditional Expression" — SingleNegationElimination, Oct 15 '11 at 14:34

score 12 · Accepted Answer · answered Oct 15 '11 at 14:26

12

Yes, the conditional expression is available in Python 2.5+:

return n if n <= 1 else fibo(n-1) + fibo(n-2)

answered Oct 15 '11 at 14:26

phihag

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things to note are that the condition is in the middle of the python version of this. C-like languages have ` ? : ` but python has the more fluent ` if else ` – SingleNegationElimination Oct 15 '11 at 14:34

Narendra Yadala · Answer 2 · 2011-10-16T01:19:45.127

5

You can try this short circuit expression return n > 1 and fibo(n-1) + fibo(n-2) or n. While this is not the ternary statement, it is concise and does the job in this scenario.

edited Oct 16 '11 at 01:19

answered Oct 15 '11 at 14:33

Narendra Yadala

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I don't think this works for `n==0` – Neil G Oct 16 '11 at 00:08
@NeilG Updated my answer. Thanks for pointing out. – Narendra Yadala Oct 16 '11 at 01:20

Is There '?' Control Flow in Python?

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