[Python-Dev] Conditional Expression Resolution

Fri Sep 30 03:21:53 CEST 2005

After a long discussion I've decided to add a shortcut conditional
expression to Python 2.5.
The syntax will be
 A if C else B
This first evaluates C; if it is true, A is evaluated to give the
result, otherwise, B is evaluated to give the result.
The priorities will be such that you can write
 x = A if C else B
 x = lambda: A if C else B
 x = A if C else B if D else E
But you'd have to write
 if (A if C else B):
 [x for x in seq if (A if C else B)]
 A if (X if C else Y) else B
 (A if C else B) if D else E
Note that all these are intentionally ugly. :)
In general, 'if' and 'else' bind less tight than everything except lambda.
We will adjust the syntax of what goes inside an 'if' to disallow
lambda; currently
 if lambda: x:
is accepted but quite useless (it's always true) so this will be disallowed.
Flames, pleas to reconsider, etc., to /dev/null.
Congratulations gracefully accepted.
It's still my language! :-)
--
--Guido van Rossum (home page: http://www.python.org/~guido/)