[Tutor] making onthefly attributes persistent

[Jojo Mwebaze]

On Mon, Dec 13, 2010 at 8:44 PM, Alan Gauld <alan.gauld at btinternet.com>wrote:

>
> "Jojo Mwebaze" <jojo.mwebaze at gmail.com> wrote
>
>  Assuming i have a class bank as below .
>>
>> class bank(object):
>>  def __init__(self, bal=0):
>>      self.bal = bal
>>  def deposit(self, amount):
>>      self.bal+=amount
>>      print self.bal
>>
>> I define a method debit - which i add to the class onthefly
>>
>> bank.debit = debit
>>
>>
>> #I can also add an attribute owner
>>
>> myaccount.owner = 'jojo'
>>
>
>  My problem is how to make the added attributes, 'owner' and 'debit'
>> persistent automatically
>>
>
> If that's your only problem with this approach congratulations!
> How does your orther code know when/if these dynamic
> operations/data exist so as to use them? If they just assume
> they exist then why not just add them in the definition. Even as nulls?
>
> While Python allows you to dynamically add features to classes/objects
> its not something I would recommend unless you have a really good
> reason - not least because you bring upon yourself all sorts of problems!
>
> If you are determined to do so you can make the objects persistent
> using the approach I outline on my tutorial but adding a loop to cycle
> over the contents of dir(). But you may find that recovering the
> objects - especially if they have a mixed set of attribnutes - presents
> even more problems...
>
> IMHO This is a feature of python that should be considered unorthodox
> and only to be used when no other approach will work!
>
> HTH,
>
>
>

Thanks Allan for the feedback, the idea is to write a method like store() on
the object, that probably looks up all these changes and commits them into
the database.

Please let me know where to find approach you propose in your tutorial. I
read your tutorial when i was just initiated to python, a reference would be
helpful to help me find the soln without hustle.

Cheers





> --
> Alan Gauld
> Author of the Learn to Program web site
> http://www.alan-g.me.uk/
>
>
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