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Style Q: Instance variables defined outside of __init__


On 3/19/2018 1:04 PM, Irv Kalb wrote:
> However, there is one warning that I am seeing often, an > I'm not sure about how to handle it.  The warning I see is:
> 
> "Instance attribute <instance variable name> defined outside of __init__ ..."

Style checkers are notorious for sometimes giving bad advice and being 
overly opinionated.

I think a claim that in all programs all attributes should be set *in* 
__init__, as opposed to *during* initialization, is wrong.  All 
attribute setting is side-effect from a functional view (and usually 
'bad' to a functionalist).  There is no reason to not delegate some of 
it to sub-init functions when it makes sense to do do.  There is good 
reason to do so when it makes the code easier to understand *and test*.

Example: the IDLE's options setting dialog.  Until last summer, it was 
one class* with at perhaps a thousand lines of initialization code (with 
no automated test).  To me, the dictate that they should have all been 
in the __init__ function is absurd.  Fortunately, there were about 9 
subsidiary functions.

* We split off a class for each tab, but keep the separate functions to 
create the tab page widgets and load them with current values.

> The following is a simple example.  I am creating a card class that I am using to build card games with PyGame.
> class Card():
> 
>      BACK_OF_CARD_IMAGE = pygame.image.load('images/backOfCard.png')
> 
>      def __init__(self, window, name, suit, value):
>          self.window = window
>          self.suit = suit
>          self.cardName = name + ' of ' + suit
>          self.value = value
>          fileName = 'images/' + self.cardName + '.png'
>          self.image = pygame.image.load(fileName)
>          self.backOfCardImage = Card.BACK_OF_CARD_IMAGE
> 
>          self.conceal()
> 
>      def conceal(self):
>          self.faceUp = False
> 
>      def reveal(self):
>          self.faceUp = True

If the single line is all these functions do, I *might* suggest getting 
rid of them.  But this is really a separate issue.

-- 
Terry Jan Reedy