类和列表的Python编程问题

我用Python编写代码，一个bug让我注意到了这一点

比如，我有这个代码：

class test1(object):
    def __init__(self):
        self.hello = ["hello"]
        self.text_back = test2().stuff(self.hello)
        print "With list:   ",self.hello[0], self.text_back[0]

class test2(object):
    def stuff(self,text1):
        self.asdf = text1
        self.asdf[0] = "goodbye"
        return self.asdf

a = test1()

#---------------

class test3(object):
    def __init__(self):
        self.hello = "hello"
        self.text_back = test4().stuff(self.hello)
        print "Without list:",self.hello, self.text_back

class test4(object):
    def stuff(self,text1):
        self.asdf = text1
        self.asdf = "goodbye"
        return self.asdf

b = test3()

输出为：

With list:    goodbye goodbye
Without list: hello goodbye

---

我有两个相同的代码，除了一个是列表，一个不是。为什么会得到不同的结果？

在代码中，我们并没有为列表创建新变量，我们只是创建引用变量名

演示：

通常复制列表：

>>> l1 = [1,2,3]
>>> l2 = l1[:]
>>> id(l1), id(l2)
(3071912556L, 3071912972L)
>>> l1.append(4)
>>> l1
[1, 2, 3, 4]
>>> l2
[1, 2, 3]
>>> 

嵌套数据结构：

>>> l1 = [1,2, [1,2], [3,4]]
>>> l2 = l1[:]
>>> l1.append(4)
>>> l1
[1, 2, [1, 2], [3, 4], 4]
>>> l2
[1, 2, [1, 2], [3, 4]]
>>> l1[2].append(3)
>>> l1
[1, 2, [1, 2, 3], [3, 4], 4]
>>> l2
[1, 2, [1, 2, 3], [3, 4]]
>>> 

Python中的深度副本

>>> import copy
>>> l1 = [1,2, [1,2], [3,4]]
>>> l2 = copy.deepcopy(l1)
>>> l1.append(4)
>>> l1[2].append(3)
>>> l1
[1, 2, [1, 2, 3], [3, 4], 4]
>>> l2
[1, 2, [1, 2], [3, 4]]
>>> 

>>> import copy
>>> l1 = [1,2, [1,2], [3,4]]
>>> l2 = copy.deepcopy(l1)
>>> l1.append(4)
>>> l1[2].append(3)
>>> l1
[1, 2, [1, 2, 3], [3, 4], 4]
>>> l2
[1, 2, [1, 2], [3, 4]]
>>>