Pythonのメタクラスを使ってフィールドが定義された順番を保持する

metaclasses_sample.py

import itertools

class _BaseValidator(object):
    _counter = itertools.count()

    def __new__(cls, *args, **kw):
        validator = object.__new__(cls)
        validator._order = next(cls._counter)
        return validator

class _ValidatorMeta(type):
    validators = []
    def __init__(cls, name, bases, clsattrs):
        for name, value in clsattrs.items():
            if isinstance(value, _BaseValidator):
                delattr(cls, name)
                if not value.name:
                    value.name = name
                cls.validators.append((value._order, value))
        cls.validators.sort()

BaseValidator = _ValidatorMeta(
    'BaseValidator',
    (_BaseValidator,),
    {}
)


class SampleDataFrame(object):
    id = BaseValidator()
    name = BaseValidator()
    age = BaseValidator()

if __name__ == '__main__':
    hoge = SampleDataFrame()
    print("id:   ", hoge.id._order)
    print("name: ", hoge.name._order)
    print("age:  ", hoge.age._order)

# $ python3 metaclasses_sample.py
# id:   0
# name: 1
# age:  2