On Wednesday, April 6, 2011 3:21:42 PM UTC-4, Νικόλαος Κούρας wrote: > On 6 Απρ, 19:58, "eryksun ()" <ery...@gmail.com> wrote: > > > The expression ``x or y`` first evaluates *x*; if *x* is > > true, its value is returned; otherwise, *y* is evaluated > > and the resulting value is returned. > > I doesnt matter if *y* is True or False before its value is returned? > *y*'s value returned no matter if its true or false?
In general *y* is an expression that gets evaluated down to some object that gets returned: In [1]: type(False or (3-3)) Out[1]: <type 'int'> In this case the int equals 0, which is False in a boolean context: In [2]: bool(False or (3-3)) Out[2]: False > >Since 'mail is None' and None evaluates to False > > What does the expression "None evaluates to false" mean in simpler > words? Every expression is evaluated at the end as True or False? It means bool(None) is False. In (x or y), the expression y will only be evaluated if bool(x) is False. If bool(x) evaluates to True, then the operation short circuits to return x without evaluating y. -- http://mail.python.org/mailman/listinfo/python-list
