python - 类的特殊成员

class Foo:
    #构造方法
    def __init__(self,name,age):
        pass
        self.name = name
        self.age = age
 
    def __str__(self):
        return "%s - %d" %(self.name,self.age)

obj1 = Foo('alex',73)
obj2 = Foo('eric',84)
print(obj1)

out:
alex - 73

__getitem__

class Foo:
    #构造方法
    def __init__(self,name,age):
        pass
        self.name = name
        self.age = age
    def __getitem__(self, item):
        return 123
 
obj = Foo('alex',73)
ret = obj['ab']
print(ret)

out:

123

class Foo:
    #构造方法
    def __init__(self,name,age):
        pass
        self.name = name
        self.age = age
    def __getitem__(self, item):
        print(item.start)
        print(item.stop)
        print(item.step)
        print(type(item),item)
 
obj = Foo('alex',73)
 
ret2 = obj[1:4:2]

out:

1
4
2

<class 'slice'> slice(1, 4, 2)

__setitem__

class Foo:
    #构造方法
    def __init__(self,name,age):
        pass
        self.name = name
        self.age = age
    def __getitem__(self, item):
        return 123
 
    def __setitem__(self, key, value):
        print('setitem')
 
obj = Foo('alex',73)
obj['k1'] = 111

out:

setitem

class Foo:
    #构造方法
    def __init__(self,name,age):
        pass
        self.name = name
        self.age = age
 
    def __setitem__(self, key, value):
        print(type(key),type(value))
        print(key.start)
        print(key.stop)
        print(key.step)
 
obj = Foo('alex',73)
 
obj[1:4] = [11,22,33,44]

out:

<class 'slice'> <class 'list'>
1
4
None

__delitem__

class Foo:
    #构造方法
    def __init__(self,name,age):
        pass
        self.name = name
        self.age = age
 
    def __delitem__(self, key):
        print('del item')
 
obj = Foo('alex',73)
 
del obj['k1']

out:

del item

class Foo:
    #构造方法
    def __init__(self,name,age):
        pass
        self.name = name
        self.age = age
 
    def __delitem__(self, key):
        print(type(key))
        print(key.start)
        print(key.stop)
        print(key.step)
 
obj = Foo('alex',73)
 
del obj[1:4]

out:

<class 'slice'>
1
4
None