That syntax looks like it's intended to communicate that f(x) is the normal result, and g(y) is exceptional. I wouldn't want to use it unless that's what I intended to communicate. It also looks like you would need to put parens around the "if" expression if you were to use it within a more complex expression, e.g

 2 + (f(x) if a else g(y)) + 3

And before Python 2.5, people usually used this idiom:

    x = a and f(x) or g(y)

If you know the idiom, I think this is more readable (conditional is on the left), though it has the drawback of using completely nonsensical keywords.

I don't think the keywords are nonsensical.

   (or (and a (f x))
       (g y))

Another drawback I just noticed is that if f(x) returns false, you'll get g(y) even if a is true.

Thanks, I didn't know that. That makes parenthesis optional unless you need to break precedence rules.