python常用魔法方法

In [1]:
#其实__str__相当于是str()方法 而__repr__相当于repr()方法。str是针对于让人更好理解的字符串格式化，而repr是让机器更好理解的字符串格式化。
class Test():
    def __init__(self,word):
        self.word=word
    def __str__(self):
        return "My name is %s" % self.word
    def __repr__(self):
        return "My name is %s" % self.word

a=Test('jack')
print(str(a))
print(repr(a))
My name is jack
My name is jack


In [2]:
#__hash__()  hash()函数的装饰器
class Test(object):
    def __init__(self, world):
        self.world = world

x = Test('world')
p = Test('world')
print(hash(x) == hash(p))
print(hash(x.world) == hash(p.world))
#以上是hash函数的用法，用于获取对象的哈希值
class Test2(object):
    def __init__(self, song):
        self.song = song

    def __hash__(self):
        return 1241
x = Test2('popo')
p = Test2('janan')
print(x, hash(x))
print(p, hash(p))
False
True
<__main__.Test2 object at 0x05E4E790> 1241
<__main__.Test2 object at 0x05E4E7F0> 1241

In [4]:
#__getattr__()   一旦我们尝试访问一个并不存在的属性的时候就会调用，而如果这个属性存在则不会调用该方法。
class Test(object):
    def __init__(self, world):
        self.world = world

    def __getattr__(self, item):
        return '不存在的属性'


x = Test('jack')
print(x.world1)
不存在的属性

In [5]:
#__setattr__()  所有设置参数属性的方法都必须经过这个魔法方法
class Test(object):
    def __init__(self, world):
        self.world = world
    def __setattr__(self, name, value):  
        #判断变量名
        if name == 'world':
            object.__setattr__(self, name, value+'!')
        else:
            object.__setattr__(self, name, value)

app=Test('jack')
print(app.world)
app.world='Tom'
print(app.world)
jack!
Tom!

In [6]:
#__delattr__() 
class Test(object):
    def __init__(self, world):
        self.world = world

    def __delattr__(self, item):
        object.__delattr__(self, item)

app=Test('jack')
print(app.world)   
del app.world
print(app.world)
jack
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-6-46b34955fb6c> in <module>
     10 print(app.world)
     11 del app.world
---> 12 print(app.world)

AttributeError: 'Test' object has no attribute 'world'

In [11]:
#__getattribute__()  拦截所有的属性获取
class Test(object):
    def __init__(self, world):
        self.world = world

    def __getattribute__(self, item):
        print('获取: %s' % item)
        return '失败'

app=Test('jack')
print(app.world)
app1=Test('Tom')
print(app.world)
获取: world
失败
获取: world
失败