How to customize getattr(obj, prop) function ?

bruno at modulix onurb at xiludom.gro
Thu May 18 12:22:16 CEST 2006


Pierre wrote:
> I don't want to use getattr(object, property, default_value) because
> I'm using external code and I don't want to modify or patch it. In this
> code, the call is getattr(object, property).

Seems like a perfectly valid reason !-)

> On my objects, I must provide default values depending on the property
> that was requested, the default value is not always the same.

On what does it depends ? Attribute name ? Class ? Phase of the moon ?

> And Yes I understand that obj.a is equivalent to getattr(obj, 'a') BUT
> the difference between class attribute and instance attribute... :S

If you mean you don't understand the difference between a class
attribute and an instance attribute, then it would be time to learn
Python's OO 101 - else you're in for trouble.

For short, an instance attribute has a per-instance value and is
(usually) stored in the object's __dict__, while a class attribute is
shared by all instances of the class and is (usually) stored in the
class's __dict__.


class Parrot(object):
  cls_attr = 'class attribute'

  def __init__(self):
    self.instance_attr = 'instance attribute'

import pprint
pprint.pprint(Parrot.__dict__.items())
p = Parrot()
pprint.pprint(p.__dict__.items())

print Parrot.cls_attr
try:
    print Parrot.instance_attr
except AttributeError, e:
    print e
# will lookup 'cls_attr' in p, then in Parrot
print p.cls_attr
print p.instance_attr

# will create an instance attribute 'cls_attr' in
# object p, shadowing Parrot.cls_attr
p.cls_attr = 'WTF ?'
print p.cls_attr
print Parrot.cls_attr

del p.cls_attr
print p.cls_attr
print Parrot.cls_attr

HTH
-- 
bruno desthuilliers
python -c "print '@'.join(['.'.join([w[::-1] for w in p.split('.')]) for
p in 'onurb at xiludom.gro'.split('@')])"



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