old_contents: # django imports
  from django.utils.translation import ugettext_lazy as _
  from django.db import models
  
  # lfs imports
  from lfs.plugins import OrderNumberGenerator as Base
  
  
  class OrderNumberGenerator(Base):
      """Generates order numbers and saves the last one.
  
      **Attributes:**
  
      id
          The primary key of the order number.
  
      last
          The last stored/returned order number.
  
      format
          The format of the integer part of the order number.
      """
      id = models.CharField(primary_key=True, max_length=20)
      last = models.IntegerField(_(u"Last order number"), default=0)
      format = models.CharField(blank=True, max_length=20)
  
      def get_next(self, formatted=True):
          """Returns the next order number.
  
          **Parameters:**
  
          formatted
              If True the number will be returned within the stored format.
          """
          self.last += 1
          self.save()
          if formatted:
              return self.format % self.last
          else:
              return self.last
  
new_contents: # django imports
  from django.utils.translation import ugettext_lazy as _
  from django.db import models
  
  # lfs imports
  from lfs.plugins import OrderNumberGenerator as Base
  
  
  class OrderNumberGenerator(Base):
      """Generates order numbers and saves the last one.
  
      **Attributes:**
  
      id
          The primary key of the order number.
  
      last
          The last stored/returned order number.
  
      format
          The format of the integer part of the order number.
      """
      id = models.CharField(primary_key=True, max_length=20)
      last = models.IntegerField(_(u"Last order number"), default=0)
      format = models.CharField(blank=True, max_length=20)
  
      def get_next(self, formatted=True):
          """Returns the next order number.
  
          **Parameters:**
  
          formatted
              If True the number will be returned within the stored format.
          """
          self.last += 1
          self.save()
          if formatted and self.format:
              return self.format % self.last
          else:
              return self.last
  
subject: Check whether there is a format given (this must be checked for validity though).