Python 20个魔法函数

本文将为您详细介绍Python中的20个魔法函数，这些函数能够在代码中释放神奇的力量。让我们一起来了解这些特殊的函数，并提供一些在实际接口自动化工作中的示例代码。魔法函数（Magic Methods），也被称为特殊方法或双下划线方法，是Python中一些特殊命名的函数，它们以双下划线开头和结尾。这些函数定义了对象在特定情况下的行为，例如创建、比较、运算、迭代等。

以下是20个常用的魔法函数及其功能的详细解释和示例代码：

__init__(self[, args...])：对象初始化函数，在创建对象时调用。

class MyClass:    def __init__(self, name):        self.name = nameobj = MyClass("Alice")

 

__str__(self)：返回对象的字符串表示。

class Point:    def __init__(self, x, y):        self.x = x        self.y = y    def __str__(self):        return f"({self.x}, {self.y})"p = Point(3, 4)print(p)  # 输出: (3, 4)

 

__len__(self)：返回对象的长度。

class MyList:    def __init__(self, items):        self.items = items    def __len__(self):        return len(self.items)my_list = MyList([1, 2, 3, 4, 5])print(len(my_list))  # 输出: 5

 

__getitem__(self, key)：获取对象的指定元素。

class MyList:    def __init__(self, items):        self.items = items    def __getitem__(self, index):        return self.items[index]my_list = MyList([1, 2, 3, 4, 5])print(my_list[2])  # 输出: 3

 

__setitem__(self, key, value)：设置对象的指定元素。

class MyList:    def __init__(self, items):        self.items = items    def __setitem__(self, index, value):        self.items[index] = valuemy_list = MyList([1, 2, 3, 4, 5])my_list[2] = 10print(my_list.items)  # 输出: [1, 2, 10, 4, 5]

 

__delitem__(self, key)：删除对象的指定元素。

class MyList:    def __init__(self, items):        self.items = items    def __delitem__(self, index):        del self.items[index]my_list = MyList([1, 2, 3, 4, 5])del my_list[2]print(my_list.items)  # 输出: [1, 2, 4, 5]

 

__contains__(self, item)：判断对象是否包含指定元素。

class MyList:    def __init__(self, items):        self.items = items    def __contains__(self, item):        return item in self.itemsmy_list = MyList([1, 2, 3, 4, 5])print(3 in my_list)  # 输出: True

 

__iter__(self)：返回迭代器对象。

class MyList:    def __init__(self, items):        self.items = items    def __iter__(self):        return iter(self.items)my_list = MyList([1, 2, 3, 4, 5])for item in my_list:    print(item)  # 依次输出: 1, 2, 3, 4, 5

 

__next__(self)：返回迭代器的下一个元素。

class MyList:    def __init__(self, items):        self.items = items        self.index = 0    def __iter__(self):        return self    def __next__(self):        if self.index >= len(self.items):            raise StopIteration        value = self.items[self.index]        self.index += 1        return valuemy_list = MyList([1, 2, 3, 4, 5])for item in my_list:    print(item)  # 依次输出: 1, 2, 3, 4, 5

 

__eq__(self, other)：判断两个对象是否相等。

class Point:    def __init__(self, x, y):        self.x = x        self.y = y    def __eq__(self, other):        return self.x == other.x and self.y == other.yp1 = Point(3, 4)p2 = Point(3, 4)print(p1 == p2)  # 输出: True

 

__lt__(self, other)：判断一个对象是否小于另一个对象。

class Point:    def __init__(self, x, y):        self.x = x        self.y = y    def __lt__(self, other):        return self.x < other.x and self.y < other.yp1 = Point(2, 3)p2 = Point(3, 4)print(p1 < p2)  # 输出: True

 

__gt__(self, other)：判断一个对象是否大于另一个对象。

class Point:    def __init__(self, x, y):        self.x = x        self.y = y    def __gt__(self, other):        return self.x > other.x and self.y > other.yp1 = Point(3, 4)p2 = Point(2, 3)print(p1 > p2)  # 输出: True

 

__add__(self, other)：定义对象的加法操作。

class Vector:    def __init__(self, x, y):        self.x = x        self.y = y    def __add__(self, other):        return Vector(self.x + other.x, self.y + other.y)v1 = Vector(1, 2)v2 = Vector(3, 4)result = v1 + v2print(f"({result.x}, {result.y})")  # 输出: (4, 6)

 

__sub__(self, other)：定义对象的减法操作。

class Vector:    def __init__(self, x, y):        self.x = x        self.y = y    def __sub__(self, other):        return Vector(self.x - other.x, self.y - other.y)v1 = Vector(3, 4)v2 = Vector(1, 2)result = v1 - v2print(f"({result.x}, {result.y})")  # 输出: (2, 2)

 

__mul__(self, other)：定义对象的乘法操作。

class Point:    def __init__(self, x, y):        self.x = x        self.y = y    def __mul__(self, factor):        return Point(self.x * factor, self.y * factor)p = Point(2, 3)result = p * 2print(f"({result.x}, {result.y})")  # 输出: (4, 6)

 

__call__(self[, args...])：使对象可调用。

class Calculator:    def __call__(self, a, b):        return a + bcalc = Calculator()result = calc(3, 4)print(result)  # 输出: 7

 

__enter__(self) 和 __exit__(self, exc_type, exc_value, traceback)：定义上下文管理器。

class FileManager:    def __init__(self, filename):        self.filename = filename    def __enter__(self):        self.file = open(self.filename, 'r')        return self.file    def __exit__(self, exc_type, exc_value, traceback):        self.file.close()with FileManager("example.txt") as file:    contents = file.read()    print(contents)

 

__getattr__(self, name)：在访问不存在的属性时调用。

class Person:    def __getattr__(self, name):        return f"Attribute '{name}' does not exist."p = Person()print(p.age)  # 输出: Attribute 'age' does not exist.

__setattr__(self, name, value)：在设置属性值时调用。class Person:    def __setattr__(self, name, value):        print(f"Setting attribute '{name}' to '{value}'")        super().__setattr__(name, value)p = Person()p.name = "Alice"  # 输出: Setting attribute 'name' to 'Alice'

 

__delattr__(self, name)：在删除属性时调用。

class Person:    def __delattr__(self, name):        print(f"Deleting attribute '{name}'")        super().__delattr__(name)p = Person()del p.name  # 输出: Deleting attribute 'name'