On Jan 13, 1:01 am, Miles <semantic...@gmail.com> wrote: > On Tue, Jan 13, 2009 at 12:02 AM, imageguy <imageguy1...@gmail.com> wrote: > > Using py2.5.4 and entering the following lines in IDLE, I don't really > > understand why I get the result shown in line 8. > > > Note the difference between lines 7 and 10 is that 'else' clause > > result enclosed in brackets, however, in line 2, both the 'c,d' > > variables are assign correctly without the brackets being required. > > > 1) >>> n = None > > 2) >>> c,d = n if n is not None else 0,0 > > 3) >>> print c,d, type(c), type(d) > > 4) 0 0 <type 'int'> <type 'int'> > > The ternary expression has higher precedence than the comma, so the > actual effect of line 2 (and 8) is: > > >>> c, d = (n if n is not None else 0), 0 > > Or written more explicitly: > > >>> c = n if n is not None else 0 > >>> d = 0 > > So the only correct way to write the expression, for the result you > want, is to use your line 10: > > > 10) >>> c,d = n if n is not None else (0,0) > > But if you're struggling with the precedence issues, I'd recommend > ditching ternary expressions altogether and using full conditional > blocks. > > -Miles
Thanks. Hadn't thought through the operator precedence and the affect of the comma. This was the first time I tried to use with tuples, so will be more careful next time or stick to control blocks. g. -- http://mail.python.org/mailman/listinfo/python-list
