Python面向对象之反射

合集 - Python学习笔记(41)

1.如何更好的学习Python2023-12-102.Python准备之Python环境安装和Pycharm使用2023-12-063.Python准备之笔记-MarkDown格式及云端笔记2023-12-064.Python准备之软件开发规范2023-12-165.Python基础之计算机基础2023-12-066.Python基础之编程语言2023-12-067.Python基础之Python基本构成2023-12-068.Python基础之流程控制2023-12-069.Python特殊机制之垃圾回收机制2023-12-0610.Python中级之数据类型的内置方法2023-12-0611.Python中级之可变数据类型和不可变数据类型2023-12-0612.Python中级之文件操作2023-12-0713.Python中级之列表字典推导式和三元运算符2023-12-0614.Python中级之深浅拷贝2023-12-0615.Python中级之字符编码2023-12-0616.Python中级之异常处理2023-12-1017.Python中级之解压赋值2023-12-1618.Python高级之闭包函数2023-12-1219.Python高级之函数介绍2023-12-1220.Python高级之名称空间与作用域2023-12-1221.Python高级之装饰器2023-12-1322.Python高级之模块与包2023-12-1623.Python高级之迭代器与生成器2023-12-1524.Python模块之re模块2023-12-3025.Python模块之os模块2024-01-0226.Python模块之random模块2024-01-0227.Python模块之序列化模块(json模块与pickle模块)2024-01-0128.Python模块之time模块和datetme模块2024-01-0129.Python高级之递归函数2024-01-0430.Python高级之常见的内置函数2024-01-0331.Python模块之sys模块2024-01-0332.Python模块之hashlib模块2024-01-0233.Python模块之logging模块2024-01-0934.Python面向对象之面向对象编程2024-01-0935.Python面向对象之三大特征-封装2024-01-1136.Python面向对象之绑定方法和非绑定方法2024-01-1137.Python面向对象之三大特征-继承2024-01-1138.Python面向对象之三大特征-多态2024-01-1239.Python面向对象之派生2024-01-1240.Python面向对象之组合2024-01-12

41.Python面向对象之反射2024-01-15

收起

本文目录

• 【一】概要
• 【二】常用方法
• 【三】详解

反射

回到顶部

【一】概要

• 在Python中，反射指的是通过字符串来操作对象的属性，涉及四个内置函数的使用（Python中一切皆对象，类和对象都可以用）

回到顶部

【二】常用方法

• getattr(object, name[, default])
  • 获取对象的属性值，如果属性不存在，可提供默认值。
• hasattr(object, name)
  • 判断对象是否具有指定属性
• setattr(object, name, value)
  • 设置对象的属性值
• delattr(object, name)
  • 删除对象的属性

回到顶部

【三】详解

【1】getattr(object, name[, default]):获取对象的属性值

• 源码解释

"""
    getattr(object, name[, default]) -> value
    
    Get a named attribute from an object; getattr(x, 'y') is equivalent to x.y.
    When a default argument is given, it is returned when the attribute doesn't
    exist; without it, an exception is raised in that case.
"""
 

• 代码解释

class Person:
    eyes = 2
 
    def __init__(self, name, age):
        self.name = name
        self.age = age
 
        
'''实例化对象'''
p = Person('user', 20)
 
res = getattr(p, 'eyes')
res1 = getattr(p, 'name')
print(res)  # 2
print(res1)  # user
 
'''如果是不存在的属性，且不指定默认值，将会报错'''
# res2 = getattr(p,'gender')
# print(res2)   # AttributeError: 'Person' object has no attribute 'gender'
 
'''设置默认值'''
res3 = getattr(p, 'gender', 'male')
print(res3)  # male   # 可以拿到默认值
print(p.__dict__)   # {'name': 'user', 'age': 20}   # 但是并不会添加到名称空间中
 
res4 = getattr(p, 'name', '001')   # 如果属性已经存在，将拿到原本的数据
print(res4)  # user

'''getattr的函数用法'''
class Person:
    eyes = 2
 
    def __init__(self, name, age):
        self.name = name
        self.age = age
 
    def func(self):
        print('from func')
 
    def func_exists(self):
        print('from func_exists')
 
 
p = Person('user', 20)
res = getattr(p, 'func')  # 可以通过getattr来获取函数内存地址调用
print(res)  # <bound method Person.func of <__main__.Person object at 0x000001D4A96CB910>>
res()  # from func
 
'''函数用法2：可以将不存在的函数名，通过指定内存地址，打印出'''
res1 = getattr(p, 'func_not', p.func_exists)
print(res1)  # <bound method Person.func_exists of <__main__.Person object at 0x000002EA0BA0B910>>
res1()  # from func_exists
 

• 应用场景

class School(object):
    def fault(self):
        print("from fault")
 
    def not_fault(self):
        print("cant fund func")
 
 
s = School()
s.fault()
'''当调用一个不存在的属性时，正常调用将会报错'''
# s.true()  # AttributeError: 'School' object has no attribute 'true'
'''如果不存在，将会输出我们指定的内容'''
res = getattr(s, 'true', s.not_fault)
res()
'''如果存在，将正常的输出函数'''
res1 = getattr(s, 'fault', s.not_fault)
res1()  # from fault

【2】hasattr(object, name)：判断对象是否具有指定属性

• 源码解释

"""
Return whether the object has an attribute with the given name.
 
This is done by calling getattr(obj, name) and catching AttributeError.
"""

• 代码解释

'''返回布尔值'''
class School(object):
    def func(self):
        print("from func")
 
 
s = School()
res = hasattr(s, 'func')
print(res)  # True
res1 = hasattr(s, 'index')
print(res1)  # False

【3】setattr(object, name, value)：设置对象的属性值

• 源码解释

"""
    Sets the named attribute on the given object to the specified value.
    
    setattr(x, 'y', v) is equivalent to ``x.y = v''
"""

• 代码解释

class School(object):
    def func(self):
        print("from func")
 
 
def index():
    print("from outer func.index")
 
 
s = School()
'''如果已经存在，将会替换'''
res = setattr(s, 'func', 'func.index')  # 替换成字符串'func.index'
print(res)  # None # 没有返回值
'''如果不存在，将会新增'''
setattr(s, 'index', index)  # 新增一个函数
print(s.__dict__)
# {'func': 'func.index', 'index': <function index at 0x0000026360D73EB0>}
s.index()  # from outer func.index

【4】delattr(object, name)：删除对象的属性

• 源码解释

"""
Deletes the named attribute from the given object.
 
delattr(x, 'y') is equivalent to ``del x.y''
"""

• 代码解释

class School(object):
    name = 'school'
 
    def func(self):
        print("from func")
 
 
print(School.name)# school
School.func(self=School())  # from func
print(School.__dict__)
# {'__module__': '__main__', 'name': 'school', 'func': <function School.func at 0x00000138D71027A0>, ...}
 
'''删除属性值'''
delattr(School, 'name')
delattr(School, 'func')
print(School.__dict__)
# {'__module__': '__main__', ...}
 
'''调用删除后的值，将会报错'''
print(School.name)   # AttributeError: type object 'School' has no attribute 'name'
School.func(School())