On Thursday, October 9, 2014 9:39:07 PM UTC+5:30, Ian wrote: > On Wed, Oct 8, 2014 at 8:34 PM, Rustom Mody wrote: > > On Thursday, October 9, 2014 7:12:41 AM UTC+5:30, Ben Finney wrote: > >> Seymore4Head writes: > >> > I want to toggle between color="Red" and color="Blue" > >> It's good to cultivate ongoing familiarity with the standard library > > And language. In recent python3: > >>>> class Color(Enum): > > ... Red = 0 > > ... Blue = 1 > > ... > >>>> Color.Red > >>>> print (Color.Red) > > Color.Red > > # Not sure what to make of that distinction... > >>>> c=Color.Red > >>>> c = Color.Blue if c==Color.Red else Color.Red > >>>> c > >>>> # Better > >>>> def toggle(c): return Color.Blue if c==Color.Red else Color.Red > > ... > >>>> toggle(c) > >>>> toggle(c) > > # which means the c has not changed
> Python enums can have methods and properties, which means that toggle > could be implemented as such: > >>> class Color(Enum): > ... red = 0 > ... blue = 1 > ... def toggle(self): > ... return Color.blue if self is Color.red else Color.red > ... > >>> Color.blue.toggle() > >>> Color.blue.toggle().toggle() Nice! In fact this: > >>> Color.blue.toggle() > <Color.red: 0> > >>> Color.blue.toggle().toggle() > <Color.blue: 1> is a nice example of a pattern that is rarely seen: OO syntax, functional (ie non-state-changing) semantics. It would have been even nicer were this acceptable [Its not :-( ] >>> class Color(Enum): ... red = 0 ... blue = 1 ... def toggle(self): ... return blue if self is red else red > (Note the recommended way to compare enum instances is with "is", not "==".) Umm... I know... Im in Lent -- fasting off contentious territories. [You may remember that I'd rather avoid 'is'] -- https://mail.python.org/mailman/listinfo/python-list
