Johnny Lee wrote:
> Hi,
> Look at the follow command in python command line, See what's
> interesting?:)
>
>
>>>>class A:
>
> i = 0
>
>>>>a = A()
>>>>b = A()
>>>>a.i = 1
>>>>print a.i, b.i
>
> 1 0
Quite what I would expect. First you declare i as being a *class*
attribute of A, with value 0. Then you create 2 instances a and b of A.
Then you add to a an *instance* variable named i (that then shadows the
class variable of the same name), with value 1. Then you print a.i,
wihci is the instance variable i of a, and b.i, which is the class
variable i of A, with value 0.
> ---------------------------------------
>
>
>>>>class A:
>
> arr = []
>
>>>>a = A()
>>>>b = A()
>>>>a
>
> <__main__.A instance at 0x00C96698>
>
>>>>b
>
> <__main__.A instance at 0x00CA0760>
>
>>>>A
>
> <class __main__.A at 0x00B314B0>
>
>>>>a.arr.append("haha")
>>>>print a.arr , b.arr
>
> ['haha'] ['haha']
Now you create a class A with a *class* variable arr which is an empty
list, and 2 instances a and b of A. Then you append to a.arr - which is
A.arr, so when you print a.arr and b.arr, you in fact print A.arr
>>>>a.arr = ["xixi"]
Then you add an instance variable arr to a, shadowing A.arr
>>>>print a.arr , b.arr
>
> ['xixi'] ['haha']
So now you print a.arr and A.arr (accessed thru b)
(snip)
>
>>>>class X:
>
> def __init__(self):
> self.arr = []
>
>>>>m = X()
>>>>n = X()
>>>>m.arr.append("haha")
>>>>print m.arr, n.arr
>
> ['haha'] []
>
Here you define a class X with an *instance* variable arr, and two
instances m and n of X, then append to m.arr, which of course has no
impact on n.
I dont see anything interesting nor problematic here. If you understand
the difference between class attributes and instance attributes, the
difference between mutating an object and rebinding a name, and the
attribute lookup rules in Python, you'll find that all this is the
normal and expected behavior.
Or did I miss something ?
--
bruno desthuilliers - is Python much more readable than Perl ???
python -c "print '@'.join(['.'.join([w[::-1] for w in p.split('.')]) for
p in '[EMAIL PROTECTED]'.split('@')])"
--
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