python的反射机制

反射机制: 让对象告诉我们它的相关信息(对象拥有的属性和方法， 对象所属的类， 这个类是否有某个属性或者方法等等)

1). 对象拥有的属性和方法

li = [1,2,3,4]
print(dir(li))

结果：

['__add__', '__class__', '__contains__', '__delattr__', '__delitem__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__gt__', '__hash__', '__iadd__', '__imul__', '__init__', '__init_subclass__', '__iter__', '__le__', '__len__', '__lt__', '__mul__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__reversed__', '__rmul__', '__setattr__', '__setitem__', '__sizeof__', '__str__', '__subclasshook__', 'append', 'clear', 'copy', 'count', 'extend', 'index', 'insert', 'pop', 'remove', 'reverse', 'sort']

我们随便写一个类来测试类的属性，方法等

import random
class Turtle(object):
    """
    乌龟类
    """
    # 构造函数什么时候执行? =---=====创建对象时执行
    def __init__(self):  # self指的是实例化的对象；
        # 乌龟的属性: x,y轴坐标和体力值
        # 乌龟的x轴， 范围1，10

        self.x = random.randint(1, 10)
        self.y = random.randint(1, 10)
        # 乌龟初始化体力为100
        self.power = 100

    # 类的方法:
    def move(self):
        # 乌龟的最大移动能力为2,[-2, -1, 0, 1, 2]
        move_skill = [-2, -1, 0, 1, 2]
        # 计算出乌龟的新坐标(10, 12)
        new_x = self.x + random.choice(move_skill)
        new_y = self.y + random.choice(move_skill)

        # 对于新坐标进行检验， 是哦否合法， 如果不合法， 进行处理
        self.x = self.is_vaild(new_x)
        self.y = self.is_vaild(new_y)

        # 乌龟每移动一次，体力消耗1
        self.power -= 1

    def is_vaild(self, value):
        """
        判断传进来的x轴坐标或者y轴坐标是否合法?

        1). 如果合法， 直接返回传进来的值；
        2). value<=0;  =====> abs(value);
        3). value > 10 ======> 10-(value-10);

        :param value:
        :return:
        """
        if 1 <= value <= 10:
            return value
        elif value < 1:
            return abs(value)
        else:
            return 10 - (value - 10)

    def eat(self):
        """
        当乌龟和鱼坐标重叠，乌龟吃掉鱼，乌龟体力增加20
        :return:
        """
        self.power += 20
turtle = Turtle()

print(dir(turtle))

结果：

['__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', 'eat', 'is_vaild', 'move', 'power', 'x', 'y']

2. 判断对象所属的类

a = [1,2,3,4]
print(type(a)) #<class ‘list’>
print(type(turtle))# <class ‘main.Turtle’>

from datetime import date
d = date(2018, 1,1)
print(type(d)) #<class ‘datetime.date’>

print(isinstance(1, str))#False
print(isinstance(turtle, Turtle))#True

3. 根据魔术方法来获取

print(turtle.class)#<class ‘main.Turtle’>
print(turtle.dict)#{‘x’: 10, ‘y’: 10, ‘power’: 100}
print(turtle.doc)#乌龟类

4. hasattr， getattr, setattr, delattr

print(hasattr(turtle, ‘x’))# True
print(hasattr(turtle, ‘x1’))# False
print(getattr(turtle, ‘x’))# 3
print(getattr(turtle, ‘x1’))#AttributeError: ‘Turtle’ object has no attribute ‘x1’

setattr(turtle, ‘x’, ‘100’)
print(getattr(turtle, ‘x’)) # 100
delattr(turtle, ‘x’)
print(hasattr(turtle, ‘x’)) # False

反射机制与模块相关的小案例

def run():

    # 用户输入url地址： http://www.baidu.com/news/index
    # 用户输入url地址： http://www.baidu.com/bbs/login
    modules, func = input('url:').split('/')[-2:]  # 获取目录的倒数两个， 即 bbs login
    # print(modules, func)
    # 倒入一个包含变量的模块名， 其中obj就是导入模块的别名
    obj = __import__('lib.'+  modules)
    print(obj)
    if hasattr(obj, func):
        return getattr(obj, func)()
    else:
        return '404:页面找不到'

if __name__ == '__main__':
    while True:
        print(run())

例2

"""
 https://www.youkuaiyun.com/nav/newarticles
 https://www.youkuaiyun.com/nav/watchers
 https://www.youkuaiyun.com/nav/news
 https://www.youkuaiyun.com/nav/ai
 https://www.youkuaiyun.com/bbs/newarticles
 https://www.youkuaiyun.com/bbs/watchers
 https://www.youkuaiyun.com/bbs/news
 https://www.youkuaiyun.com/bbs/ai
"""
class Web(object):
    def bbs(self):
        return "<h1>bbs</h1>"

    def news(self):
        return "<h1>news</h1>"

    def music(self):
        return "<h1>music</h1>"

    def movie(self):
        return "<h1>movie</h1>"
    # 假设下面还有50个
def run():
    flask = Web()
    # 用户输入url地址： http://www.baidu.com/news
    url = input('url:').split('/')[-1]
    if hasattr(flask, url):
        return getattr(flask, url)()
    else:
        return '404'


if __name__ == '__main__':
    while True:
        print(run())