old_contents: from django.db import models
  from django.template.defaultfilters import timesince
  
  class Person(models.Model):
      class Meta:
          verbose_name = 'Persona'
  
      name = models.TextField(verbose_name='Nombre')
      surname = models.TextField(verbose_name='Apellidos')
      birthday = models.DateField(verbose_name='Fecha de nacimiento', blank=True, null=True)
      id_number = models.TextField(verbose_name='DNI/NIE', blank=True, default='')
      ss_number = models.TextField(verbose_name='Tarjeta sanitaria', blank=True, default='')
      address_street = models.TextField(verbose_name='Dirección', blank=True, default='')
      address_locality = models.TextField(verbose_name='Localidad', blank=True, default='')
      address_region = models.TextField(verbose_name='Provincia', blank=True, default='')
      address_country = models.TextField(verbose_name='País', blank=True, default='')
      phone_number = models.TextField(verbose_name='Teléfono', blank=True, default='')
      email = models.EmailField(verbose_name='Correo electrónico', blank=True, default='')
      comment = models.TextField(verbose_name='Observaciones', blank=True, default='')
      health_warnings = models.TextField(verbose_name='Observaciones médicas', blank=True, default='')
  
      @property
      def age(self):
          return timesince(self.birthday)
  
      def __str__(self):
          return '{} {}'.format(self.name.capitalize(), self.surname.upper())
  
  
  class Group(models.Model):
      class Meta:
          verbose_name = 'Grupo'
  
      group_name = models.TextField(verbose_name='Nombre grupo')
  
      def __str__(self):
          return self.group_name
new_contents: from django.db import models
  from django.template.defaultfilters import timesince
  
  
  class Person(models.Model):
      class Meta:
          verbose_name = 'Persona'
  
      name = models.TextField(verbose_name='Nombre')
      surname = models.TextField(verbose_name='Apellidos')
      birthday = models.DateField(verbose_name='Fecha de nacimiento', blank=True, null=True)
      id_number = models.TextField(verbose_name='DNI/NIE', blank=True, default='')
      ss_number = models.TextField(verbose_name='Tarjeta sanitaria', blank=True, default='')
      address_street = models.TextField(verbose_name='Dirección', blank=True, default='')
      address_locality = models.TextField(verbose_name='Localidad', blank=True, default='')
      address_region = models.TextField(verbose_name='Provincia', blank=True, default='')
      address_country = models.TextField(verbose_name='País', blank=True, default='')
      phone_number = models.TextField(verbose_name='Teléfono', blank=True, default='')
      email = models.EmailField(verbose_name='Correo electrónico', blank=True, default='')
      comment = models.TextField(verbose_name='Observaciones', blank=True, default='')
      health_warnings = models.TextField(verbose_name='Observaciones médicas', blank=True, default='')
  
      @property
      def age(self):
          return timesince(self.birthday)
  
      def __str__(self):
          return '{} {}'.format(self.name.capitalize(), self.surname.upper())
  
  
  class Group(models.Model):
      class Meta:
          verbose_name = 'Grupo'
  
      group_name = models.TextField(verbose_name='Nombre grupo')
  
      def __str__(self):
          return self.group_name
  
subject: Corrige formateo según PEP8