为什么1 .__ add __(2)无法解决? [英] Why does 1.__add__(2) not work out?

问题描述

可能重复:
访问python int文字方法

Possible Duplicate:
accessing a python int literals methods

在Python中，everything is an object.

但是再说一遍，为什么以下代码段不起作用?

But then again, why doesn't the following snippet work?

1.__add__(2)

但是，这确实可行:

n = 1
n.__add__(2)

n和1有什么区别?

这不是设计失败吗? 例如，它也适用于string文字.

Isn't it a design failure that it doesn't work? For instance, it does work with string literals as well.

"one".__add__("two")

为了进行比较，它也可以在其他纯面向对象的语言上很好地工作.

For comparison, it works well on other purely object oriented languages too.

让我们仔细看一下这个编译的c#示例:

Let's take a closer look at this compiling c# example:

Console.WriteLine(100.ToString());

那么，从everything is an object的角度来看，Python与C#有何区别?

Then again, what distinguishes Python from C# in the perspective of everything is an object?

推荐答案

Python的解析器故意非常简单-它强制实施的约束之一是，要弄清楚令牌的含义，它只能看一个令牌右侧(它是 LL(1)解析器).

Python's parser is deliberately very simple - one of the constraints it enforces on itself is that, to figure out what a token means, it can only look one token to the right (it is an LL(1) parser).

因此，它看到[number] [dot]，并确定它是浮点文字. '_'不是浮点文字中的有效字符，因此会出现语法错误.

So, it sees [number][dot], and determines that it is a floating point literal. '_' isn't a valid character to have in a floating point literal, so it gives a syntax error.

克服此问题的最明显，最常见的方法是将数字放在括号中:

The most obvious and most common way to overcome this is to put the number in parentheses:

(1).__add__(2)

这将迫使它在解析器的限制内将1解释为整数文字，并将点解释为属性访问权限.

This forces it to interpret the 1 as an integer literal, and the dot as attribute access, within the limitations of the parser.

另一个有趣的解决方法是:

Another interesting workaround is this:

>>> 1 .__add__(2) 
3

即，在.之前添加一个空格.事实证明，Python总是在其中留出空间来存储任何属性:

That is, add a space before the .. It turns out that Python always allows a space there for any attribute lookup:

>>> range(4) .count(3)
1

我发现这很令人惊讶，但是Python似乎在与+相似的规则下对待.，因此将在其周围留出尽可能多的空间.

I found this quite surprising, but it seems that Python treats . under similar rules to +, and so will allow as much space as you like around it.

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