# python version >= 3.6

def definegetters(klass):
    for name, type_ in klass.__annotations__.items():
        default = getattr(klass, name, type_())
        # デフォルト引数にコピーしないとループで変数が上書きされる
        def _getter(self, private='_'+name, default=default):
            try:
                return getattr(self, private)
            except AttributeError:
                setattr(self, private, default)
                return getattr(self, private)
        exec(f'klass.{name} = property(_getter)')
    return klass

@definegetters
class Foo:
    # 変数へのアノテーション(3.6から)
    spam: int
    ham: str
    eggs: bool = True

    def __init__(self):
        self._ham = 'example'

if __name__ == '__main__':
    foo = Foo()
    print(repr(foo.spam))  # => 0
    print(repr(foo.ham))   # => 'example'
    print(repr(foo.eggs))  # => True
    foo._spam = 100
    print(repr(foo.spam))  # => 100