Earlier quoted context omitted.
I'd rather have Python's way of doing it, which plays with the order for the sake of readability: useful_metric = complex_calc(foo) if want_complex_calc else simple_calc(foo)
Ruby has something similar, and I can't stand it. I think the conditional is the most important item in the phrase, and it's shoved off to the right. If you lead with the conditional, it becomes immediately apparent that the assignment is predicated on the result of a branch.
Ruby (and Python) likely get that from Perl, which has post conditionals, but with specific qualities to prevent them from too much abuse, and which also prevents them from being used in the way presented here (which is why I didn't trot them out earlier, as much as I was tempted by the "you write what you mean" line). The limitations are that there is no else branch, and it only applies to a single statement, so you can't have a block executed with a post conditional. It leads to usage like so:
die "Invalid param: please enter a positive number" unless $param1 > 0;
$param2 = 0 unless defined $param2;
return undef if $param1 and not $param2;
my $foo = 1 if $bar; # This unfortunately creates a closure around $foo and is a big source of bugs.