Python学习基础笔记六十四——Item系列

1、getitem/setitem/delitem系统：

class Foo:
    def __init__(self, name, age, sex):
        self.name = name
        self.age = age
        self.sex = sex

    def __getitem__(self, item):
        if hasattr(self, item):
            return self.__dict__[item]

    def __setitem__(self, key, value):
        self.__dict__[key] = value

    def __delitem__(self, key):
        self.__dict__[key]


f = Foo(egon, 38, 男)
print(f[name])
f[hobby] = 男

print(f[hobby], f.hobby)

# del f.hobby

print(f.__dict__)
del f[hobby]
print(f.__dict__)

2、new例：

class A:
    def __init__(self):
        self.x = 1
        print(in init function)
    def __new__(cls, *args, **kwargs):
        print(in new function)
        return object.__new__(A)

a = A()
print(a.x)

3、单例模式：

class Singleton:
    def __new__(cls, *args, **kw):
        if not hasattr(cls, _instance):
            cls._instance = object.__new__(cls)
        return cls._instance

one = Singleton()
two = Singleton()

two.a = 3
print(one.a)
# 3
# one和two完全相同,可以用id(), ==, is检测
print(id(one))
# 29097904
print(id(two))
# 29097904
print(one == two)
# True
print(one is two)

3、__eq__

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

    def __eq__(self, other):
        if self.name == other.name:
            return True
        else:
            return False


obj1 = A(eggon)
obj2 = A(egg)

print(obj1 == obj2)

4、__hash__

class A:
    def __init__(self):
        self.a = 1
        self.b = 2

    def __hash__(self):
        return hash(str(self.a)+str(self.b))
a = A()
print(hash(a))