How to use patterns in the definition of a variable in Django

Question

I am working in Django and I have the following class

class Usuario(AbstractBaseUser):
username            =models.CharField(verbose_name='Nombre de usuario', max_length=45, unique=True)

date_join           =models.DateTimeField(verbose_name='Fecha de alta', auto_now_add=True)
last_login          =models.DateTimeField(verbose_name='Última conexión', auto_now=True)
es_docente          =models.BooleanField(default=False)
es_estudiante       =models.BooleanField(default=False)
es_directivo        =models.BooleanField(default=False)
es_preceptor        =models.BooleanField(default=False)
es_tutor            =models.BooleanField(default=False)
es_superuser        =models.BooleanField(default=False)
estado              =models.BooleanField(default=True)

now, I would like to add a function to change the boolean states, if it is possible, by using some kind of pattern. I know that the following code is wrong but I didn't find the correct syntax:

def changer(self,var):
     es_(%var) = not Usuario.es_(%var)

where I am marking with %var some kind of usage of the input of the function. For example, I would like to input changer(preceptor) and receive as output that the changing of the boolean field es_preceptor.

Thanks in advance!