除了这里的其他优秀答案之外，++和——也因未定义的行为而臭名昭著。例如，这段代码中发生了什么?

foo[bar] = bar++;

它看起来很无辜，但它是错误的C(和c++)，因为您不知道第一个栏是否会增加。一个编译器可能会以一种方式执行，另一个可能会以另一种方式执行，而第三个编译器可能会让恶魔从你的鼻子里飞出来。所有这些都完全符合C和c++标准。

(编辑:c++ 17改变了给定代码的行为，这样它就被定义了;它将等价于foo[bar+1] = bar;+ +酒吧;——尽管如此，这可能不是程序员所期望的。)

在C和c++中，未定义行为被视为不可避免的邪恶，但在Python中，它只是邪恶，并尽可能避免。

Maybe a better question would be to ask why do these operators exist in C. K&R calls increment and decrement operators 'unusual' (Section 2.8page 46). The Introduction calls them 'more concise and often more efficient'. I suspect that the fact that these operations always come up in pointer manipulation also has played a part in their introduction. In Python it has been probably decided that it made no sense to try to optimise increments (in fact I just did a test in C, and it seems that the gcc-generated assembly uses addl instead of incl in both cases) and there is no pointer arithmetic; so it would have been just One More Way to Do It and we know Python loathes that.

它就是这样设计的。自增和自减运算符只是x = x + 1的快捷方式。Python通常采用一种设计策略，减少执行操作的可选方法的数量。增强赋值是Python中最接近自增/自减操作符的东西，它们直到Python 2.0才被添加。

这并不是因为它没有意义;将“x++”定义为“x+ = 1，求值到x的前一个绑定”非常有意义。

如果你想知道最初的原因，你必须在旧的Python邮件列表中寻找，或者询问当时在那里的人(例如。Guido)，但事后很容易就能证明:

简单的递增和递减不需要像其他语言那样多。你不会写这样的for(int i = 0;I < 10;i)在Python中经常使用;相反，你可以把I放在(0,10)范围内。

由于不经常需要它，所以没有理由给它自己的特殊语法;当您确实需要增加时，+=通常就可以了。

It's not a decision of whether it makes sense, or whether it can be done--it does, and it can. It's a question of whether the benefit is worth adding to the core syntax of the language. Remember, this is four operators--postinc, postdec, preinc, predec, and each of these would need to have its own class overloads; they all need to be specified, and tested; it would add opcodes to the language (implying a larger, and therefore slower, VM engine); every class that supports a logical increment would need to implement them (on top of += and -=).

这些都是+=和-=的冗余，所以会变成净损失。

操作符的++类是带有副作用的表达式。这在Python中通常是找不到的。

出于同样的原因，赋值在Python中不是表达式，从而防止使用here */}习语来使用常见的if (a = f(…)){/*。

最后，我怀疑这些操作符与python的引用语义不太一致。请记住，Python没有C/ c++中已知语义的变量(或指针)。

其他答案描述了为什么迭代器不需要它，但有时它在赋值以inline增加变量时很有用，你可以使用元组和多次赋值达到相同的效果:

B = ++a变成:

a,b = (a+1,)*2

b = a++变成:

a,b = a+1, a

Python 3.8引入了赋值:=操作符，允许我们用

foo(a:=a+1)

Foo (a++)仍然是难以捉摸的。