Am 13.12.2010 23:50, schrieb Jojo Mwebaze:
On Mon, Dec 13, 2010 at 8:44 PM, Alan Gauld <alan.ga...@btinternet.com
<mailto:alan.ga...@btinternet.com>> wrote:
"Jojo Mwebaze" <jojo.mweb...@gmail.com
<mailto:jojo.mweb...@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.
Assuming you're planning to use a database with a scheme (e.g. a
relational DB) you need to define your tables in advance anyway. Even if
you're using a schemeless DB, where do you track which data is in it?
How do you build your queries dynamically? This can become very messy.
Overall, I think Alan's recommendation to avoid dynamic attribute
creation is the one to follow.
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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