[Tutor] global variables/constants versus volatile variables/constants

[diliup gabadamudalige]

Thank you very much Allan! 100% clear.
I thank each and every one of you who contributed to all my question on the
above subject.
A lot of things became very clear.
May you all be well.



On Sun, Jun 15, 2014 at 3:15 AM, Alan Gauld <alan.gauld at btinternet.com>
wrote:

> On 14/06/14 13:53, diliup gabadamudalige wrote:
>
>  Say if I have a lot of Lists, strings and variables used to carry data
>> to and from various functions why can't I have a class with all these in
>> it?
>>
>
> You can but it should also have the functions that operate on the data
> too. Thats the point of classes they link function and data together
> so you don't need to pass lots of parameters around. If you have a class
> that jusat holds lots of disparate data items you might as well just use a
> list/tuple or dictionary. The value of classes is when you add behaviour or
> methods to the mix.
>
>
>
>  I thought on the lines of blood carrying various things to different
>> organs in the body.
>>
>
> But even there the blood has a distinct set of related items, it doesn't
> carry the food to your stomach or the video signals from
> your eye to your brain. And blood has operations - it can flow,
> coagulate, increase/decrease red-cell count etc. It has
> behaviour as well as data.
>
>
>  class Containers():
>>      def __init__(self):
>> self.last_selected_scale= ""
>> self.scale_notes = ""
>> self.arpeggionotes = ""
>> self.handplayed_notes = []
>> self.MIDIscale = []  # the MIDI scale to be played is here
>> self.play_MIDIscale = False
>> self.play_MIDIarpeggio = False
>> self.play_MIDI_scale_note = False
>> self.play_MIDI_arpeggio_note = False
>> self.MIDInote_inscale = 0
>>
>
> Now that could be a Tune... And it might have record/play/pause operations
>
>
>
>  now say if I play the MIDI keyboard, I collect the notes played which
>> will be appended to the list v.hanplayednotes. This will be done from a
>> function which will scan the keyboard and append played notes to that
>> list.
>>
>
> But that could be a method of the Tune sub-class, MidiTune, which knows
> how to record from a MidiSequencer object.
>
>
>  This is how I have used these variables, lists and strings in this
>> program. So far it has run error free.
>>
>
> The issue is not how to make it run - you can do that in assembler.
> The issue is how easy is it to read and how easy os it to modify and fix
> later. 80% of the cost of commercial software is in "maintenance"
> The goal of professional software engineers is to reduce maintenance
> costs even if that increases the initial 20% development budget.
>
>
>  Is this not correct or bad design. I know it is not the normal way of
>> using class but is it wrong?
>>
>
> Almost certainly, because it adds a layer of complexity for little or no
> gain.
>
> Whereas adding the methods to the class improves the maintainability and
> readability (and sometimes the performance, although that's a secondary
> benefit).
>
> HTH
>
> --
> Alan G
> Author of the Learn to Program web site
> http://www.alan-g.me.uk/
> http://www.flickr.com/photos/alangauldphotos
>
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-- 
Diliup Gabadamudalige

http://www.diliupg.com
http://soft.diliupg.com/

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