Question

list = []和list.clear()有什么区别？

根据我的代码的行为和我自己的观察，list.clear()除去其条目以及用于附加其数据的条目。

示例：

container.append(list)
list.clear()

container也将是[]

Answer 1

调用clear将从列表中删除所有元素。分配[]只是将该变量替换为另一个空列表。当您有两个指向同一列表的变量时，这一点变得明显。

请考虑以下代码段：

>>> l1 = [1, 2, 3]
>>> l2 = l1
>>> l1.clear()
>>> l1 # l1 is obviously empty
[]
>>> l2 # But so is l2, since it's the same object
[]

与此相比：

>>> l1 = [1, 2, 3]
>>> l2 = l1
>>> l1 = []
>>> l1 # l1 is obviously empty
[]
>>> l2 # But l2 still points to the previous value, and is not affected
[1, 2, 3]

Answer 2

如果您查看生成的字节码，也可以看到此信息。这里带有x = []

的部分

import dis

print("Exmaple with x = []")

s1 = """
x = [1,2,3]
x = []
"""

dis.dis(s1)

输出

Exmaple with x = []
  2           0 LOAD_CONST               0 (1)
              2 LOAD_CONST               1 (2)
              4 LOAD_CONST               2 (3)
              6 BUILD_LIST               3
              8 STORE_NAME               0 (x)

  3          10 BUILD_LIST               0
             12 STORE_NAME               0 (x)
             14 LOAD_CONST               3 (None)
             16 RETURN_VALUE

由于我们有两个BUILD_LIST，因此我们可以看到构建了两个列表。现在，我们来看看x.clear()

print("Exmaple with x.clear()")

s2 = """
x = [1,2,3]
x.clear()
"""

dis.dis(s2)

我们得到以下输出

Exmaple with x.clear()
  2           0 LOAD_CONST               0 (1)
              2 LOAD_CONST               1 (2)
              4 LOAD_CONST               2 (3)
              6 BUILD_LIST               3
              8 STORE_NAME               0 (x)

  3          10 LOAD_NAME                0 (x)
             12 LOAD_ATTR                1 (clear)
             14 CALL_FUNCTION            0
             16 POP_TOP
             18 LOAD_CONST               3 (None)
             20 RETURN_VALUE

此处仅构建了一个列表，并调用了clear，并且使用LOAD_CONST将None与初始值1,2,3一样放置在堆栈上。

list = []与list.clear（）之间的区别

2 个答案: