Python入門 面向對象

簡單Try

class Student(object):
    def __init__(self, name, score):
        self.name=name
        self.score = score

    def print_score(self):
        print("%s %s" %(self.name, self.score))


dd = Student('draymonder', 21)
bb = Student('bing', 21)

dd.print_score()

訪問限制

若是要讓內部屬性不被外部訪問，能夠把屬性的名稱前加上兩個下劃線__，在Python中，實例的變量名若是以__開頭，就變成了一個私有變量（private），只有內部能夠訪問，外部不能訪問

其實是能夠訪問的，只是_規範程序員以私有變量來使用
具體訪問以下

class Student(object):
    def __init__(self, name, score):
        self.__name=name
        self.__score = score

    def print_score(self):
        print("%s %s" %(self.__name, self.__score))


dd = Student('draymonder', 21)
print(dd._Student__name)

print(dd._Student__name)

@property

內置的@property裝飾器就是負責把一個方法變成屬性調用的

class Student(object):

    @property
    def birth(self):
        return self._birth
    
    @birth.setter
    def birth(self, vale):
        self._birth = value

    @property
    def age(self):
        return 2019 - self._birth

s = Student()
s._birth = 1998
print(s.age)

getattr

class Chain(object):

    def __init__(self, path=''):
        self._path = path

    def __getattr__(self, path):
        return Chain('%s/%s' % (self._path, path))

    def __str__(self):
        return self._path

    __repr__ = __str__

print(Chain().status.user.timeline.list)

使用元類

建立類

def fn(self, name="world"):
    print("hello %s" %name)

Hello = type("hello", (object,), dict(hello=fn)) #建立hello class

list添加add方法

class ListMetaclass(type):
    def __new__(cls, name, bases, attrs):
        attrs['add'] = lambda self,value: self.append(value)
        return type.__new__(cls, name, bases, attrs)

class MyList(list, metaclass = ListMetaclass):
    pass

L = MyList()
L.add(1)
L.add(2)
L.add(3)
print(L)

簡易ORM模型

class ModelMetaclass(type):
    def __new__(cls, name, bases, attrs):
        if name=='Model':
            return type.__new__(cls, name, bases, attrs)
        print('Found model: %s' % name)
        mappings = dict()
        for k, v in attrs.items():
            if isinstance(v, Field):
                print('Found mapping: %s ==> %s' % (k, v))
                mappings[k] = v
        for k in mappings.keys():
            attrs.pop(k)
        attrs['__mappings__'] = mappings # 保存屬性和列的映射關係
        attrs['__table__'] = name # 假設表名和類名一致
        return type.__new__(cls, name, bases, attrs)


class Model(dict, metaclass=ModelMetaclass):
    def __init__(self, **kw):
        super(Model, self).__init__(**kw)

    def __getattr__(self, key):
        try:
            return self[key]
        except KeyError:
            raise AttributeError(r"'Model' object has no attribute '%s'" % key)

    def __setattr__(self, key, value):
        self[key] = value

    def save(self):
        fields = []
        params = []
        args = []
        for k, v in self.__mappings__.items():
            fields.append(v.name)
            params.append('?')
            args.append(getattr(self, k, None))
        sql = 'insert into %s (%s) values (%s)' % (self.__table__, ','.join(fields), ','.join(params))
        print('SQL: %s' % sql)
        print('ARGS: %s' % str(args))




# Field(name, column_type)
class Field(object):
    def __init__(self, name, column_type):
        self.name = name
        self.column_type = column_type

    def __str__(self):
        return "<%s:%s>" %(self.__class__.__name__, self.name)

class StringField(Field):
    def __init__(self, name):
        super(StringField, self).__init__(name, 'varchar(100)')

class IntegerField(Field):
    def __init__(self, name):
        super(IntegerField, self).__init__(name, 'bigint')

class User(Model):
    id = IntegerField("id")
    name = StringField("username")
    email = StringField("email")
    password = StringField("password")




u = User(id=1,name="draymonder",email="93958042@qq.com",password="IloveU")
u.save()

參考文章

python面向對象編程