# 运算符

## 运算符重载基础规则

- 不能重载内置类型的运算符
- 不能新建运算符，只能重载现有的运算符
- 某些运算符不能重载，如is、and、or和not

## 一元运算符

| 符号 | 方法         | 描述                                 |
| ---- | ------------ | ------------------------------------ |
| -    | `__neg__`    | 负号                                 |
| +    | `__pos__`    | 正号                                 |
| ~    | `__invert__` | 对整数按位取反，定义为`~x == -(x+1)` |
| abs  | `__abs__`    | 取绝对值运算符                       |

## 中缀运算符

| 符号        | 正向方法       | 反向方法   | 就地方法   | 描述                           |
| ----------- | -------------- | ---------- | ---------- | ------------------------------ |
| +           | `__add__`      | `__radd__` | `__iadd__` | 加法、拼接                     |
| -           | `__sub__`      | `__rsub__` | `__isub__` | 减法                           |
| *           | `__mul__`      |            |            | 乘法、重复复制                 |
| /           | `__truediv__`  |            |            | 除法                           |
| //          | `__floordiv__` |            |            | 整除                           |
| %           | `__mod__`      |            |            | 取模                           |
| `divmod()`  | `__divmod__`   |            |            | 返回元组，（整除商，取模余数） |
| `**, pow()` | `__pow__`      |            |            | 取幂                           |
| @           | `__matmul__`   |            |            | 矩阵乘法                       |
| &           | `__and__`      |            |            | 按位与                         |
| \|          | `__or__`       |            |            | 按位或                         |
| ^           | `__xor__`      |            |            | 按位异或                       |
| <<          | `__lshift__`   |            |            | 按位左移                       |
| >>          | `__rshift__`   |            |            | 按位右移                       |

## 比较运算符

| 符号   | 正向方法      | 反向方法      | 后备机制            |
| ------ | ------------- | ------------- | ------------------- |
| `a==b` | `a.__eq__(b)` | `b.__eq__(a)` | 返回 `id(a)==id(b)` |
| `a!=b` | `a.__ne__(b)` | `b.__ne__(a)` | 返回 `not (a==b)`   |
| `a>b`  | `a.__gt__(b)` | `b.__lt__(a)` | 抛出`TypeError`     |
| `a<b`  | `a.__lt__(b)` | `b.__gt__(a)` | 抛出`TypeError`     |
| `a>=b` | `a.__ge__(b)` | `b.__le__(a)` | 抛出`TypeError`     |
| `a<=b` | `a.__le__(b)` | `b.__ge__(a)` | 抛出`TypeError`     |


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