Proposed PEP for a Conditional Expression

[Tim Peters]

[Michael Chermside]
> Included in this email is a PEP which I am putting together dealing with
> the idea of introducing a conditional expression into Python.

Win, lose or draw, I want to thank you for writing this PEP!  It's long
overdue, and it will be good to settle this issue.

> ...
>          WORKAROUND_3: (this is the most common idiom)
>              > x = (c and [a] or [b])[0]
>              Here we create one-element lists and index into them.
>              Since [a] is definitely NOT false (it's got 1 element),
>              the and-or syntax will succeed.

This is frequently suggested, but almost never used.  I invented this
"idiom" for Python in the very early 90's.  It was in a joke thread, about
obfuscated Python.  Anyone using it in real code should be shot; I've never
used it (which is why I'm still alive to type this <wink>).

> Reference Implementation
>      ...
>      The implementation is not expected to be difficult at all,

Beware:  mucking with the parser isn't easy, especially as there are no
3-argument infix operators now.  Code generation is easy in this case, but
fiddling the grammar may be a pit.