Python 字符串不是不可变的吗?那么为什么一个 + ""+ 工作? [英] Aren't Python strings immutable? Then why does a + " " + b work?

问题描述

我的理解是 Python 字符串是不可变的.

My understanding was that Python strings are immutable.

我尝试了以下代码:

a = "Dog"
b = "eats"
c = "treats"

print a, b, c
# Dog eats treats

print a + " " + b + " " + c
# Dog eats treats

print a
# Dog

a = a + " " + b + " " + c
print a
# Dog eats treats
# !!!

Python 不应该阻止赋值吗?我可能遗漏了一些东西.

Shouldn't Python have prevented the assignment? I am probably missing something.

有什么想法吗?

推荐答案

第一个 a 指向字符串Dog".然后将变量 a 更改为指向一个新字符串Dog Eats Treats".您实际上并没有改变字符串Dog".字符串是不可变的，变量可以指向任何他们想要的.

First a pointed to the string "Dog". Then you changed the variable a to point at a new string "Dog eats treats". You didn't actually mutate the string "Dog". Strings are immutable, variables can point at whatever they want.

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