Python中表达式x += y和x = x+y 的区别详解

  • Z时代
  • 2024-01-10
  • 分类：综合

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:

  • += 对应 INPLACE_ADD

  • 对应BINARY_ADD

注意：以上仅适用于CPython实现。

总结

以上是 Python中表达式x += y和x = x+y 的区别详解 的全部内容， 来源链接： utcz.com/z/356086.html

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