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For review: PEP 308 - If-then-else expression

Carlos Ribeiro cribeiro at mail.inet.com.br
Sat Feb 8 16:24:59 EST 2003 
On Saturday 08 February 2003 02:11 pm, Michele Simionato wrote:
> [snip]
> ...
> or the more pythonic "when"
>
>  if (when callable(obj) obj() else default):
>
> would be less confusing. I think introducing a ternary operator is
> worthwhile but one needs a new keyword to avoid confusion
> with the "if" statement.

Lets us two ways to write conditional expressions using 'when':

1) if (when callable(obj): obj() else default):

-> In this case, I think that the colon is needed after the condition; it does 
not seem right to have the condition and the true branch right next to each 
other without some explicit delimiter. The comma would work fine here.

-> As far as I understand it, this proposal requires 'when' to become a 
reserved identifier; this makes it less likely to be accepted. On the other 
hand, I think that few programs would ever use a variable named 'when', so 
this problem may be irrelevant in the end.


2) if (obj() when callable(obj) else default):

-> This one follows the steps of Guido's proposal, but it looks a little bit 
better than the original proposal, as it does not reuse 'if'. In this case, 
the colon seem to be out of place, and I think it's better without it.

-> In this case I believe that 'when' does not need to be a reserved 
identifier. But I'm not aware of all the details involved, I'm just working 
with analogies to other constructs.


In both cases, I think that the parenthesis makes the expression clearer. In 
my opinion, it should be required.

And last... the else clause has to be required. I don't see any sense in 
having an implicit default value for it - it breaks the spirit of the 
conditional operator (btw, it's not called 'ternary operator' by some people 
without any reason, isn't it?)


Carlos Ribeiro
cribeiro at mail.inet.com.br
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