[Python-ideas] Updating PEP 315: do-while loops
rrr at ronadam.com
Sun Apr 26 06:44:16 CEST 2009
Larry Hastings wrote:
> Ron Adam wrote:
>> I'd prefer a bare "while:" with a more visible "break if" and possibly
>> "continue if" expressions.
> I do like "break if" and "continue if", unsurprisingly as I suggested
> them in parallel. I'm not sure about the "while:"; your "while: ...
> continue if ; break" strikes down some of the clarity we're trying to
> achieve here.
The bare "while:" can be a completely separate issue.
continue if condition
I'm not sure why you think that is less or not clear. It's just an
possible to do if you add 'continue if'. <shrug>
The equivalent would be:
break if (not condition)
But this reverses the test and that could express what you are doing in a
less clear way. Being able to do it both ways is a good thing I think.
If you allow the if-else syntax to be used with flow control keywords then
you have 6 possibilities.
break if condition else pass
break if condition else continue
continue if condition else pass
continue if condition else break
pass if condition else break
pass if condition else continue
It makes sense to shorten some of these..
break if condition # 'else pass' doesn't do anything
continue if condition # ""
I'm not sure the others are needed, they may allow some problems to be
expressed more explicitly.
The nice thing about extending python this way is these expressions may
also work in for loops and possibly other places.
Because python is based as much on practical need rather than just what is
possible to do. We may only need the two last shorter versions above.
But I won't complain if all six of the longer versions above also work. ;-)
In anycase Raymond was asking for ideas that are consistent with pythons
syntax and I think these suggestions are. The one inconsistant thing is
if-else expressions normally return a value, and in these cases, they
either should raise a syntax error or return None if they are used on the
right hand side of an expression.
More information about the Python-ideas