Some syntactic sugar proposals

Tim Chase python.list at
Mon Nov 15 13:46:59 CET 2010

On 11/15/2010 12:39 AM, Dmitry Groshev wrote:
> x in range optimisation

I've often thought this would make a nice O(1)-test lookup on an 
xrange() generator.  I don't have strong use-cases for it, but a 
bit of well-tested code in the standard library would save me 
from doing the math (along with its potential fenceposting and 
sign errors) the couple times I've reached for it.  Using the

   x in list(xrange(...)) # or "range()" depending your version

ends up with an O(n) lookup, though I suppose one could create a 
set() for O(1) lookups, but that still requires O(N) storage 
(where a mathematical lookup would involve O(1) storage *and* time)

> foo() if foo() else bar()

This is usually indicative that you need to cache the 
object...something like

   etcc = expensive_to_calculate_constructor()
   result = foo(etcc) if test(etcc) else bar()

That way, you cache the potentially-expensive calculation, 
indicate to other readers-of-your-code that it's 
potentially-expensive, and enforce the use of that cache to 
ensure that you don't duplicate the expensive op.


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