时间：2021-01-06 11:22:15 | 栏目：Python代码 | 点击：次
前言
本文主要给大家介绍的是关于Python中表达式x += y和x = x+y 区别的相关内容，分享出来供大家参考学习，下面来看看详细的介绍：
直接看下面代码:
x +=y
In [66]: id(a) Out[66]: 4476839480 In [67]: id(b) Out[67]: 4476839480 In [68]: a = [1, 2, 3] In [69]: b = a In [70]: id(a) Out[70]: 4477149984 In [71]: id(b) Out[71]: 4477149984 In [72]: a += [4, 5, 6] In [73]: a Out[73]: [1, 2, 3, 4, 5, 6] In [74]: b Out[74]: [1, 2, 3, 4, 5, 6] In [75]: id(a) Out[75]: 4477149984 In [76]: id(b) Out[76]: 4477149984
x = x + y
In [77]: a = [1, 2, 3] In [78]: b = a In [79]: id(a) Out[79]: 4476686208 In [80]: id(b) Out[80]: 4476686208 In [81]: a = a + [4, 5, 6] In [82]: a Out[82]: [1, 2, 3, 4, 5, 6] In [83]: b Out[83]: [1, 2, 3] In [84]: id(a) Out[84]: 4477187640 In [85]: id(b) Out[85]: 4476686208
可以看出对于可变对象而言 x = x + y 这种形式已经改变了x的指向，而不是"inplace"的修改。
使用dis模块进行一下验证。
In [86]: def foo(x, y):
...: x += y
...: return x
...:
In [87]: def foo(x, y):
...: x += y
...:
In [88]: def foo2(x, y):
...: x = x + y
...:
In [89]: dis.dis(foo)
2 0 LOAD_FAST 0 (x)
3 LOAD_FAST 1 (y)
6 INPLACE_ADD
7 STORE_FAST 0 (x)
10 LOAD_CONST 0 (None)
13 RETURN_VALUE
In [90]: dis.dis(foo2)
2 0 LOAD_FAST 0 (x)
3 LOAD_FAST 1 (y)
6 BINARY_ADD
7 STORE_FAST 0 (x)
10 LOAD_CONST 0 (None)
13 RETURN_VALUE
可以看到字节码是不同的:
注意：以上仅适用于CPython实现。
总结