(My apologies if the thread has already covered this.) I believe I understand
the WHAT in this situation, but I don't understand the WHY ...
Given this class definition:
class Cls(object):
x = 345
... I observe the following, using IDLE 2.6.1:
>>> inst = Cls()
>>> Cls.x is inst.x
True
>>> Cls.x += 1
>>> Cls.x is inst.x
True
>>> inst.x += 1
>>> Cls.x is inst.x
False
My question is ... WHY does the interpreter silently create the instance
attribute at this point, causing a "surprising decoupling" from the class
attribute? WHY doesn't the interpreter behave as it would with a simple,
non-instance variable:
> python
Python 2.6.1 ...
Type "help", "copyright", "credits" or "license" for more information.
>>> x += 1
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
NameError: name 'x' is not defined
Is there a beneficial effect of silently creating the instance attribute, which
outweighs the detrimental effects: (1) inconsistency, (2) the "surprising"
decoupling?
Tx,
John
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