Stupid Lambda Tricks [LONG]

[Luigi Ballabio]

Hi,

At 09:51 AM 2/21/02 +0000, Gerson Kurz wrote:
>* Using IF statements
>
>4.16. Is there an equivalent of C's "?:" ternary operator?

<snip>

>This method is of course trivially defined as lambda:
>
>IF = lambda a,b,c:(a and [b] or [c])[0]

I wouldn't advise using anything of the sort of your IF thing, because it 
doesn't short-circuit. Try this:

def a():
     return 1
def b():
     print "lengthy b() calculation, possibly with side effects"
def c():
     print "lengthy c() calculation, possibly with side effects"

# Use the ternary trick:
 >>> (a() and [b()] or [c()])[0]
lengthy b() calculation, possibly with side effects

# Use you IF thing instead:
 >>> IF(a(),b(),c())
lengthy b() calculation, possibly with side effects
lengthy c() calculation, possibly with side effects

Bye,
         Luigi