# 特殊方法

运算符无关特殊方法

| 类别            | 方法                                                         |
| --------------- | ------------------------------------------------------------ |
| 字符串/字节序列 | `__repr__`, `__str__`, `__format__`, `__bytes__`             |
| 数值转换        | `__abs__`, `__bool__`, `__complex__`, `__init__`, `__float__`, `__hash__`, `__index__` |
| 集合模拟        | `__len__`, `__getitem__`, `__setitem__`, `__delitem__`, `__contains__` |
| 迭代枚举        | `__iter__`, `__reversed__`, `__next__`                       |
| 可调用模拟      | `__call__`                                                   |
| 上下文管理      | `__enter__`, `__exit__`                                      |
| 实例创建和销毁  | `__new__`, `__init__`, `__del__`                             |
| 属性管理        | `__getattr__`, `__setattr__`, `__delattr__`, `__dir__`       |
| 属性描述符      | `__get__`, `__set__`, `__delete__`                           |
| 类判断          | `__prepare__`, `__instancecheck__`, `__subclasscheck__`      |

运算符相关的特殊方法

| 类别       | 运算符    | 方法           |
| ---------- | --------- | -------------- |
| 一元运算符 | -         | `__neg__`      |
|            | +         | `__pos__`      |
|            | abs()     | `__abs__`      |
| 比较运算符 | <         | `__lt__`       |
|            | <=        | `__le__`       |
|            | ==        | `__eq__`       |
|            | !=        | `__ne__`       |
|            | >         | `__gt__`       |
|            | >=        | `__ge__`       |
| 算数运算符 | +         | `__add__`      |
|            | -         | `__sub__`      |
|            | *         | `__mul__`      |
|            | /         | `__truediv__`  |
|            | //        | `__floordiv__` |
|            | %         | `__mod__`      |
|            | divmod()  | `__divmode__`  |
|            | **或pow() | `__pow__`      |
|            | round()   | `__round__`    |
|            |           |                |

# `__repr__` 和`__str__`

`__repr__` 和`__str__` 能将一个对象用字符串形式表达。当输出一个对象时，默认会调用`repr()` 函数，其调用对象的`__repr__` 方法。`__str__` 方法是在`str()` 函数被使用或者在`print()` 函数打印一个对象。一般不用实现两个特殊方法，如果一个对象没有`__str__` 方法，解释器会使用`__repr__` 方法代替。

```python
from math import hypot

class Vector():
    def __init__(self, x=0, y=0):
        self.x = x
        self.y = y
    
    def __repr__(self):
        return 'Vector(%r, %r)' % (self.x, self.y)
    
    def __abs__(self):
        return hypot(self.x, self.y)
    
    def __bool__(self):
        return bool(abs(self))
    
    def __add__(self, other):
        x = self.x + other.x
        y = self.y + other.y
        return Vector(x, y)
    
    def __mul__(self, scalar):
        return Vector(self.x*scalar, self.y*scalar)
```

# `__contains__`

在类中添加`__contains__(self, x)` 特殊方法，可以判断输入的x数据是否在对象中，对象具有容器的性质。

```python
class Graph():
    def __init__(self):
        self.items = {'a': 1, 'b': 2, 'c': 3}

    def __contains__(self, x):
        return x in self.items
    
one_ob = Graph()
print('a' in one_ob)
print('d' in one_ob)

>>>True
>>>False
```


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