第十八天——反射（一）

一.反射

反射的概念是由Smith在1982年首次提出的，主要是指程序可以访问、检测和修改它本身状态或行为的一种能力（自省）。这一概念的提出很快引发了计算机科学领域关于应用反射性的研究。它首先被程序语言的设计领域所采用,并在Lisp和面向对象方面取得了成绩。

python面向对象中的反射：通过字符串的形式操作对象相关的属性。python中的一切事物都是对象（都可以使用反射）

四个可以实现自省的函数

下列方法适用于类和对象（一切皆对象，类本身也是一个对象）

1.1 对象的反射

class Foo:
    f = '类的静态变量'
    def __init__(self,name,age):
        self.name=name
        self.age=age
<span class="token keyword">def</span> <span class="token function">say_hi</span><span class="token punctuation">(</span>self<span class="token punctuation">)</span><span class="token punctuation">:</span>
    <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">'hi,%s'</span><span class="token operator">%</span>self<span class="token punctuation">.</span>name<span class="token punctuation">)</span>

obj=Foo('egon',73)
#检测是否含有某属性

print(hasattr(obj,'name'))

print(hasattr(obj,'say_hi'))
#获取属性

n=getattr(obj,'name')

print(n)

func=getattr(obj,'say_hi')

func()
print(getattr(obj,'aaaaaaaa','不存在啊')) #报错
#设置属性

setattr(obj,'sb',True)

setattr(obj,'show_name',lambda self:self.name+'sb')

print(obj.dict)

print(obj.show_name(obj))
#删除属性

delattr(obj,'age')

delattr(obj,'show_name')

delattr(obj,'show_name111')#不存在,则报错
print(obj.dict)
对实例化对象的示例

1.2 对类的反射

class Foo(object):
staticField <span class="token operator">=</span> <span class="token string">"old boy"</span>

<span class="token keyword">def</span> <span class="token function">__init__</span><span class="token punctuation">(</span>self<span class="token punctuation">)</span><span class="token punctuation">:</span>
    self<span class="token punctuation">.</span>name <span class="token operator">=</span> <span class="token string">'wupeiqi'</span>

<span class="token keyword">def</span> <span class="token function">func</span><span class="token punctuation">(</span>self<span class="token punctuation">)</span><span class="token punctuation">:</span>
    <span class="token keyword">return</span> <span class="token string">'func'</span>

<span class="token decorator annotation punctuation">@staticmethod</span>
<span class="token keyword">def</span> <span class="token function">bar</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">:</span>
    <span class="token keyword">return</span> <span class="token string">'bar'</span>

print getattr(Foo, 'staticField')

print getattr(Foo, 'func')

print getattr(Foo, 'bar')

1.3 当前模块的反射

import sys
def s1():

print 's1'
def s2():

print 's2'
this_module = sys.modules[name]
hasattr(this_module, 's1')

getattr(this_module, 's2')

1.4 其他模块的反射

#一个模块中的代码
def test():
    print('from the test')
"""
程序目录：
    module_test.py
    index.py
当前文件：

index.py

"""

# 另一个模块中的代码

import module_test as obj
#obj.test()
print(hasattr(obj,'test'))
getattr(obj,'test')()

1.5 反射的应用

了解了反射的四个函数。那么反射到底有什么用呢？它的应用场景是什么呢？

现在让我们打开浏览器，访问一个网站，你单击登录就跳转到登录界面，你单击注册就跳转到注册界面，等等，其实你单击的其实是一个个的链接，每一个链接都会有一个函数或者方法来处理。

没学反射之前的解决方式

class User:
    def login(self):
        print('欢迎来到登录页面')
<span class="token keyword">def</span> <span class="token function">register</span><span class="token punctuation">(</span>self<span class="token punctuation">)</span><span class="token punctuation">:</span>
    <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">'欢迎来到注册页面'</span><span class="token punctuation">)</span>

<span class="token keyword">def</span> <span class="token function">save</span><span class="token punctuation">(</span>self<span class="token punctuation">)</span><span class="token punctuation">:</span>
    <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">'欢迎来到存储页面'</span><span class="token punctuation">)</span>

while 1:

choose = input('>>>').strip()

if choose == 'login':

obj = User()

obj.login()
<span class="token keyword">elif</span> choose <span class="token operator">==</span> <span class="token string">'register'</span><span class="token punctuation">:</span>
    obj <span class="token operator">=</span> User<span class="token punctuation">(</span><span class="token punctuation">)</span>
    obj<span class="token punctuation">.</span>register<span class="token punctuation">(</span><span class="token punctuation">)</span>

<span class="token keyword">elif</span> choose <span class="token operator">==</span> <span class="token string">'save'</span><span class="token punctuation">:</span>
    obj <span class="token operator">=</span> User<span class="token punctuation">(</span><span class="token punctuation">)</span>
    obj<span class="token punctuation">.</span>save<span class="token punctuation">(</span><span class="token punctuation">)</span>

学了反射之后解决方式

class User:
    def login(self):
        print('欢迎来到登录页面')
<span class="token keyword">def</span> <span class="token function">register</span><span class="token punctuation">(</span>self<span class="token punctuation">)</span><span class="token punctuation">:</span>
    <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">'欢迎来到注册页面'</span><span class="token punctuation">)</span>

<span class="token keyword">def</span> <span class="token function">save</span><span class="token punctuation">(</span>self<span class="token punctuation">)</span><span class="token punctuation">:</span>
    <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">'欢迎来到存储页面'</span><span class="token punctuation">)</span>

user = User()

while 1:

choose = input('>>>').strip()

if hasattr(user,choose):

func = getattr(user,choose)

func()

else:

print('输入错误。。。。')

这样就可以明确的感觉到反射的好处,我们一直使用的字典方式其实就是反射的思想

只不过反射比我们之前写法方法还有霸道