Miles 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. > Yet another great example of why Guido was right to resist putting conditional expressions into Python for so long (and wrong to succumb to the demand).
regards Steve -- Steve Holden +1 571 484 6266 +1 800 494 3119 Holden Web LLC http://www.holdenweb.com/ -- http://mail.python.org/mailman/listinfo/python-list
