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From: Ian Kelly <ian.g.kelly@gmail.com>
Date: Thu, 9 Oct 2014 10:07:28 -0600
Subject: Re: Toggle
To: Python <python-list@python.org>
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On Wed, Oct 8, 2014 at 8:34 PM, Rustom Mody <rustompmody@gmail.com> 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
> <Color.Red: 0>
>>>> 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
> <Color.Blue: 1>
>>>>
>
>>>> # Better
>>>> def toggle(c): return Color.Blue if c==Color.Red else Color.Red
> ...
>>>> toggle(c)
> <Color.Blue: 1>
>>>> toggle(c)
> <Color.Blue: 1>
>
> # 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.red: 0>
>>> Color.blue.toggle().toggle()
<Color.blue: 1>

(Note the recommended way to compare enum instances is with "is", not "==".)