一文带你深入理解Python魔法方法

class MyClass:
    def __new__(cls, *args, **kwargs):
        print('Instance is created')
        instance = super().__new__(cls)
        return instance
    def __init__(self, name):
        print('Instance is initialized')
        self.name = name
obj = MyClass('MyClass')  # 输出：Instance is created Instance is initialized

class MyClass:
    def __init__(self, name):
        self.name = name
    def __str__(self):
        return f'Instance of MyClass with name {self.name}'
    def __repr__(self):
        return f'MyClass(name={self.name})'
obj = MyClass('MyClass')
print(str(obj))  # 输出：Instance of MyClass with name MyClass
print(repr(obj))  # 输出：MyClass(name=MyClass)

class Number:
    def __init__(self, value):
        self.value = value
    def __add__(self, other):
        return self.value + other.value
num1 = Number(1)
num2 = Number(2)
print(num1 + num2)  # 输出：3

class Number:
    def __init__(self, value):
        self.value = value
    def __lt__(self, other):
        return self.value < other.value
num1 = Number(1)
num2 = Number(2)
print(num1 < num2)  # 输出：True

class MyClass:
    def __init__(self):
        self.name = 'MyClass'
    def __getattribute__(self, item):
        if item == 'name':
            print('Accessing name attribute')
        return object.__getattribute__(self, item)
    def __setattr__(self, key, value):
        print(f'Setting attribute {key} with value {value}')
        self.__dict__[key] = value
obj = MyClass()
print(obj.name)  # 输出：Accessing name attribute MyClass
obj.name = 'New name'  # 输出：Setting attribute name with value New name

class ManagedFile:
    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_val, exc_tb):
        if self.file:
            self.file.close()
with ManagedFile('hello.txt') as f:
    content = f.read()
print(content)