old_contents: # MIT License
  # Copyright (c) 2017 MassChallenge, Inc.
  
  from __future__ import unicode_literals
  from django.utils.encoding import python_2_unicode_compatible
  from django.conf import settings
  from django.db import models
  
  from accelerator.models.accelerator_model import AcceleratorModel
  
  
  @python_2_unicode_compatible
  class Currency(AcceleratorModel):
      name = models.CharField(max_length=64, unique=True)
      abbr = models.CharField(max_length=3, unique=True)
      usd_exchange = models.FloatField()
  
      class Meta(AcceleratorModel.Meta):
          db_table = 'accelerator_currency'
          managed = settings.ACCELERATOR_MODELS_ARE_MANAGED
  
      def __str__(self):
          return self.name
  
new_contents: # MIT License
  # Copyright (c) 2017 MassChallenge, Inc.
  
  from __future__ import unicode_literals
  from django.utils.encoding import python_2_unicode_compatible
  from django.conf import settings
  from django.db import models
  
  from accelerator.models.accelerator_model import AcceleratorModel
  
  
  @python_2_unicode_compatible
  class Currency(AcceleratorModel):
      name = models.CharField(max_length=64, unique=True)
      abbr = models.CharField(max_length=3, unique=True)
      usd_exchange = models.FloatField()
  
      class Meta(AcceleratorModel.Meta):
          db_table = 'accelerator_currency'
          managed = settings.ACCELERATOR_MODELS_ARE_MANAGED
  
      def __str__(self):
          return self.name
  
      @classmethod
      def choices(cls):
          return [(c["id"], c["name"])
                  for c in cls.objects.all().values("id", "name")]
  
      @classmethod
      def default_currency(cls):
          usd = cls.objects.filter(abbr="USD")
          if usd:
              return usd[0]
          return cls.objects.all()[0]
  
subject: add missing class methods for Currency: