Someone correct me if I'm wrong (sometimes I get the terms mixed up)
but I believe that what you are seeing is due to 'number' being an
immutable type. This means that its value cannot be changed and thus
each assignment is effectively creating a new instance if int. I
believe lists are considered immutable also but since it is a container
type it behaves somewhat differently. I read a thread earlier that
addressed a similar issue but I can't find it now. I will post again if
I come accross it. Anyway, as a demonstration try this using python's
command line prompt:
>>> i = int()
>>> j = i
>>> j is i
True
### j and i are attributes that point to the same instance
>>> i = 1
>>> j is i
False
### assignment to I made a new instance and j and i are no longer the
same instance
>>> a = [0,1,2]
>>> b = a
>>> b is a
True
### the same is true for lists
>>> b = [0,1,3]
>>> b is a
False
>>> b = a
>>> b is a
True
### but since 'a' is a container its contents can be modified without
creating a new instance
>>> b[1] = 3
>>> b is a
True
>>> a
[0,3,2]
>>> b
[0,3,2]
>>> a.append(4)
>>> a
[0,3,2,4]
>>> b
[0,3,2,4]
>>> b is a
True
I hope this helps.
-Matt
[EMAIL PROTECTED] wrote:
> Greetings again!
>
> There's something more to determining whether a class member is a class
> variable or an instance variable. Here's a slightly expanded version
> of my last script:
>
> class ScannerCommand:
> taskName = ''
> scanList = []
> number = 0
>
> def __init__(self, data):
> pass
> # self.scanList = []
> # self.scanList.append(data)
>
> if __name__ == '__main__':
> c1 = ScannerCommand("c1")
> c2 = ScannerCommand("c2")
> c1.number = 1
> c2.number = 2
> c1.scanList.append("One")
> c2.scanList.append("Two")
> print "C1: " + str(c1.number)
> for data in c1.scanList:
> print " " + data
> print "C2: " + str(c2.number)
> for data in c2.scanList:
> print " " + data
>
> And here's the output:
> C1: 1
> One
> Two
> C2: 2
> One
> Two
>
> Here, the two instances share the scanList list, as expected from
> previous discussions, but they have their own copies of the number
> variable. Why is scanList a class variable but number an instance
> variable here?
>
> Good night, all!
>
> Rob Richardson
> RAD-CON, Inc.
> Bay Village, OH
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