Python 反射(reflection)

反射是指通过字符串映射或修改程序运行时的状态、属性、方法, 有以下4个方法

1.getattr(object, name, default = None)

根据字符串获取 obj 对象里对应 str 方法的内存地址

示例：

class Dog(object):
    def __init__(self, name):
        self.name = name

    def eat(self, food):
        print('%s is eating %s' % (self.name, food))

dog1 = Dog('Dog1')
choice = input('>>').strip()
if hasattr(dog1, choice):
    getattr(dog1, choice)('bone')   # 根据字符串获取对象里对应方法的内存地址，传入‘bone’执行
    print(getattr(dog1, choice))    # 打印属性

输出结果：

>>eat

Dog1 is eating bone

<bound method Dog.eat of <__main__.Dog object at 0x00000249C4C3B780>>

2.hasattr(object, name)

判断一个 obj 对象里是否有对应 str 字符串

示例：

class Dog(object):
    def __init__(self, name):
        self.name = name

    def eat(self, food):
        print('%s is eating %s' % (self.name, food))

dog1 = Dog('Dog1')
choice = input('>>').strip()
print(hasattr(dog1, choice))        # 判断一个 obj 对象里是否有对应 str 字符串

输出结果：

>>eat

True

3.setattr(object, y, v)

给类新加了一个属性等于： obj.y = v

传入属性示例：

class Dog(object):
    def __init__(self, name):
        self.name = name

    def eat(self, food):
        print('%s is eating %s' % (self.name, food))

dog1 = Dog('Dog1')
choice = input('>>').strip()
print(hasattr(dog1, choice))        # 判断一个 obj 对象里是否有对应 str 字符串
if hasattr(dog1, choice):
    print(getattr(dog1, choice))    # 打印修改前的属性
    setattr(dog1, choice, 'Dog2')   # 如果属性存在，可以通过 setattr 进行修改
    print(getattr(dog1, choice))    # 打印修改后的属性
else:
    setattr(dog1, choice, None)     # 给类新加了一个属性 == dog1.choice = None
    print(getattr(dog1, choice))    # 打印新加入的属性

修改已有属性输出结果：

>>name

True

Dog1

Dog2

增加新的属性输出结果：

>>age

False

None

传入方法示例：

class Dog(object):
    def __init__(self, name):
        self.name = name

    def eat(self, food):
        print('%s is eating %s' % (self.name, food))

def bulk(self):                     # 传入方法需要提前写好
    print('%s: woof,woof!' % self.name)

dog1 = Dog('Dog1')
choice = input('>>').strip()
print(hasattr(dog1, choice))        # 判断一个 obj 对象里是否有对应 str 字符串
if hasattr(dog1, choice):
    pass
else:
    setattr(dog1, choice, bulk)     # 给类新加了一个方法
    dog1.bulk(dog1)                 # 调用新加入的方法 bulk

输出结果：

>>bulk

False

Dog1: woof,woof!

4.delattr(object, name)

删除 obj 对象中对应属性

示例：

class Dog(object):
    def __init__(self, name):
        self.name = name

    def eat(self, food):
        print('%s is eating %s' % (self.name, food))

dog1 = Dog('Dog1')
choice = input('>>').strip()
print(hasattr(dog1, choice))        # 输出 True
if hasattr(dog1, choice):
    delattr(dog1, choice)
    print(getattr(dog1, choice))    # 打印会报错