处理类和对象变量时python中字符串和数字的不同行为

Question

I found one issue and not able to understand the reason of difference:

code1:

class Test:
    var=2
    def __init__(self):
        self.var=self.var+1

p=Test()
print "p.var:",p.var
q=Test()
print "q.var:",q.var

output 1:

p.var:3
q.var:3

Why not the output is(According to concept used to explain code2)

p.var:3
q.var:4

Code2:

class Test:
    var=[]
    def __init__(self):
        self.var.append("fool")

p=Test()
print "p.var:",p.var
q=Test()
print "q.var:",q.var

output2:

p.var: ['fool']
q.var: ['fool', 'fool']

i read the article on code2 in Stack Exchange: python class instance variables and class variables

but not able to link code1 with the following concept.Please help

Answer 1

The difference here is that lists are mutable objects; integers are immutable. When code1 increments self.var, it must return a new object, that being 3. On the second call,we start over with 2, producing another 3 for object q .

In code2, var is still a class object (only one for the class, not one per object). When we create p , we append "fool" to the empty list. When we later create q we append a second "fool". Print them both:

p=Test2()
print "p.var1:",p.var
q=Test2()
print "q.var2:",q.var
print "p.var2:",p.var

output:

p.var1: ['fool']
q.var2: ['fool', 'fool']
p.var2: ['fool', 'fool']

Does that clarify things?