I'm personally an advocate of the ternary operator: () ? : ; I do realize that it has its place, but I have come across many programmers that are completely against ever using it, and some that use it too often.
What are your feelings on it? What interesting code have you seen using it?
Yes, it was added in version 2.5. The expression syntax is:
a if condition else b
First condition is evaluated, then exactly one of either a or b is evaluated and returned based on the Boolean value of condition. If condition evaluates to True, then a is evaluated and returned but b is ignored, or else when b is evaluated and returned but a is ignored.
This allows short-circuiting because when condition is true only a is evaluated and b is not evaluated at all, but when condition is false only b is evaluated and a is not evaluated at all.
>>> 'true' if True else 'false'
>>> 'true' if False else 'false'
Note that conditionals are an expression, not a statement. This means you can't use assignment statements or pass or other statements within a conditional expression:
>>> pass if False else x = 3
File "<stdin>", line 1
pass if False else x = 3
SyntaxError: invalid syntax
You can, however, use conditional expressions to assign a variable like so:
x = a if True else b
Think of the conditional expression as switching between two values. It is very useful when you're in a 'one value or another' situation, it but doesn't do much else.
If you need to use statements, you have to use a normal ifstatement instead of a conditional expression.
Keep in mind that it's frowned upon by some Pythonistas for several reasons:
Some find it "unwieldy", since it goes contrary to the normal flow of thought (thinking of the condition first and then the effects).
Stylistic reasons. (Although the 'inline if' can be really useful, and make your script more concise, it really does complicate your code)
If you're having trouble remembering the order, then remember that when read aloud, you (almost) say what you mean. For example, x = 4 if b > 8 else 9 is read aloud as x will be 4 if b is greater than 8 otherwise 9.
Depends upon the version. The If operator in VB.NET 2008 is a ternary operator (as well as a null coalescence operator). This was just introduced, prior to 2008 this was not available. Here's some more info: Visual Basic If announcement
Dim foo as String = If(bar = buz, cat, dog)
Prior to 2008 it was IIf, which worked almost identically to the If operator described Above.