[PYTHON/COMMON] 메타 클래스 : 특정 클래스 속성 값 자동 설정하기

■ 메타 클래스를 사용해 특정 클래스 속성 값을 자동 설정하는 방법을 보여준다.

▶ 예제 코드 (PY)


class Field:
    def __init__(self):
        self.name         = None
        self.internalName = None

    def __get__(self, instance, instanceType):
        if instance is None:
            return self
        return getattr(instance, self.internalName, "")

    def __set__(self, instance, value):
        setattr(instance, self.internalName, value)

class TableRowMeta(type):
    def __new__(metaClass, className, baseNameTuple, classMemberDictionary):
        for key, value in classMemberDictionary.items():
            if isinstance(value, Field):
                value.name         = key
                value.internalName = f"_{key}"
        classInstance = type.__new__(metaClass, className, baseNameTuple, classMemberDictionary)
        return classInstance

class TableRow(metaclass = TableRowMeta):
    pass

class Customer(TableRow):
    firstName = Field()
    lastName  = Field()
    prefix    = Field()
    sufix     = Field()

customer = Customer()

print("작업전 :", customer.firstName, customer.lastName, customer.__dict__)

customer.firstName = "길동"
customer.lastName  = "홍"

print("작업후 :", customer.firstName, customer.lastName, customer.__dict__)

"""
작업전 :   {}
작업후 : 길동 홍 {'_firstName': '길동', '_lastName': '홍'}
"""

class Field:

def __init__(self):

self.name = None

self.internalName = None

def __get__(self, instance, instanceType):

if instance is None:

return self

return getattr(instance, self.internalName, "")

def __set__(self, instance, value):

setattr(instance, self.internalName, value)

class TableRowMeta(type):

def __new__(metaClass, className, baseNameTuple, classMemberDictionary):

for key, value in classMemberDictionary.items():

if isinstance(value, Field):

value.name = key

value.internalName = f"_{key}"

classInstance = type.__new__(metaClass, className, baseNameTuple, classMemberDictionary)

return classInstance

class TableRow(metaclass = TableRowMeta):

pass

class Customer(TableRow):

firstName = Field()

lastName = Field()

prefix = Field()

sufix = Field()

customer = Customer()

print("작업전 :", customer.firstName, customer.lastName, customer.__dict__)

customer.firstName = "길동"

customer.lastName = "홍"

print("작업후 :", customer.firstName, customer.lastName, customer.__dict__)

"""

작업전 : {}

작업후 : 길동 홍 {'_firstName': '길동', '_lastName': '홍'}

"""