Python27 反射

发布时间：2019-09-16 07:34:33编辑：auto阅读（1698）

反射：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：
2.hasattr：判断一个对象里是否有对应（相同名称）字符串的方法
3.setattr
4.delattr

class Dog(object):

    def __init__(self,name):
        self.name = name

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

d = Dog('XiaoBai')
choice = input('>>:').strip()   #让用户输入项调用Dog类中的功能（方法）

d.choice()


图中输入choice的内容是一个字符串，正常调用d.eat()这可不是一个字符串。
报错提示Dog中不存在attribute choice(字符串)

class Dog(object):

    def __init__(self,name):
        self.name = name

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

d = Dog('XiaoBai')
choice = input('>>:').strip()   

print (hasattr(d,choice))   #判断对象d里是否有对应eat字符串的方法    #hasattr的全称就是hasattribute（有没有属性....)

执行结果：
>>:eat
True    #通过这种方式就可以确认在class Dog中是否存在eat功能了

执行结果：
>>:talk
False

class Dog(object):

    def __init__(self,name):
        self.name = name

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

d = Dog('XiaoBai')
choice = input('>>:').strip()

if hasattr(d,choice):   #如果d中存在eat
    getattr(d,choice)()  #就用getattr调用d.eat，后面不加括号的话就是打印内存信息了
#根据字符串去获取d对象里的方法的内存地址
执行结果：
>>:eat
XiaoBai is eating...

class Dog(object):

    def __init__(self,name):
        self.name = name

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

d = Dog('XiaoBai')
choice = input('>>:').strip()

if hasattr(d,choice):
    func = getattr(d,choice) #当前func==d.eat
    func('Bone')    #将Bone传给food参数

setattr()
我们通过ctrl点进去setattr中


x表示对象
y被引号引着表示y是字符串
x.y=v v相当于值

class Dog(object):

    def __init__(self,name):
        self.name = name

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

def bulk(self):
    print ('%s is yelling.....' %self.name)

d = Dog('XiaoBai')
choice = input('>>:').strip()

if hasattr(d,choice):
    func = getattr(d,choice)
    func('Bone')
else:
    setattr(d,choice,bulk)  #将bulk赋值给choice(这里choice=talk，也就相当于赋值给talk）
    d.talk(d)
    #这里choice=talk，这里d.talk=bulk，bulk本身是一个函数内存地址，将这个内存地址赋值给了talk，当前talk相当于bulk这个函数了，所以调用d.talk就相当于调用bulk这个函数，而d.bulk则是不存在的.

执行结果：
>>:talk
XiaoBai is yelling.....

class Dog(object):

    def __init__(self,name):
        self.name = name

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

def bulk(self):
    print ('%s is yelling.....' %self.name)

d = Dog('XiaoBai')
choice = input('>>:').strip()

if hasattr(d,choice):
    func = getattr(d,choice)
    func('Bone')
else:
    # setattr(d,choice,bulk)
    # d.talk(d)
    setattr(d,choice,22)    #建立一个新的、不存在的静态属性，赋予值22
    print (getattr(d,choice))

执行结果：
>>:age  #建立的静态属性名称为age，然后得到赋值22
22

执行结果：
>>:name     #这里输入已存在的变量名
Traceback (most recent call last):
  File "E:/Python/练习代码/A1.py", line 20, in <module>
    func('Bone')
TypeError: 'str' object is not callable
#因为name的值已经通过func = getattr(d,choice)获取了，不能通过func('Bone')这样调用

class Dog(object):

    def __init__(self,name):
        self.name = name

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

def bulk(self):
    print ('%s is yelling.....' %self.name)

d = Dog('XiaoBai')
choice = input('>>:').strip()

if hasattr(d,choice):

    setattr(d,choice,'LeLe')    #设置已有属性的值（相当于更改了）

else:
    # setattr(d,choice,bulk)
    # d.talk(d)
    setattr(d,choice,22)
    print (getattr(d,choice))

print (d.name)

执行结果：
>>:name
LeLe    #可以看到已经不是XiaoBai了，是改过的LeLe

class Dog(object):

    def __init__(self,name):
        self.name = name

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

def bulk(self):
    print ('%s is yelling.....' %self.name)

d = Dog('XiaoBai')
choice = input('>>:').strip()

if hasattr(d,choice):

    delattr(d,choice)   #删除属性

else:
    # setattr(d,choice,bulk)
    # d.talk(d)
    setattr(d,choice,22)
    print (getattr(d,choice))

print (d.name)

执行结果：
>>:name     #指定删除name这个属性
Traceback (most recent call last):
  File "E:/Python/练习代码/A1.py", line 28, in <module>
    print (d.name)
AttributeError: 'Dog' object has no attribute 'name'
#可以看到name属性已不存在

class Dog(object):

    def __init__(self,name):
        self.name = name

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

def bulk(self):
    print ('%s is yelling.....' %self.name)

d = Dog('XiaoBai')
choice = input('>>:').strip()

if hasattr(d,choice):

    getattr(d,choice)

else:
    setattr(d,choice,None)
    print (d.choice)    #这里是不能这么打印的，这里的choice只是单纯的一个叫choice的字符串，而不是choice = input输入的值。
    AA = d.choice

print (d.name)

执行结果：
>>:age
Traceback (most recent call last):
  File "E:/Python/练习代码/A2.py", line 25, in <module>
    print (d.choice)
AttributeError: 'Dog' object has no attribute 'choice'

class Dog(object):

    def __init__(self,name):
        self.name = name

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

def bulk(self):
    print ('%s is yelling.....' %self.name)

d = Dog('XiaoBai')
choice = input('>>:').strip()

if hasattr(d,choice):

    getattr(d,choice)

else:
    setattr(d,choice,None)
    AA = getattr(d,choice)      #需要先通过getattr获取这个choice的值
    print (AA)

执行结果：
>>:age
None

class Dog(object):

    def __init__(self,name):
        self.name = name

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

def bulk(self):
    print ('%s is yelling.....' %self.name)

d = Dog('XiaoBai')
choice = input('>>:').strip()

if hasattr(d,choice):

    getattr(d,choice)

else:
    setattr(d,choice,None)
    print (d.age)   #这个age就是choice=input输入的值，因为age存在所以可以直接打印
    AA = getattr(d,choice)      #需要先通过getattr获取这个choice的值
    print (AA)

执行结果：
>>:age
None    #print (d.age)
None    #print (AA)

关键字：