old_contents: from django.conf import settings
  from django.core.validators import ValidationError
  
  # A list of allowable thumbnail file extensions.
  ALLOWABLE_THUMBNAIL_EXTENSIONS = getattr(
      settings, 'ALLOWABLE_THUMBNAIL_EXTENSIONS', ['png', 'jpg', 'jpeg', 'gif'])
  
  class ImageUploadExtensionValidator(object):
      """
      Perform some basic image uploading extension validation.
      """
      compare = lambda self, a, b: a is not b
      clean   = lambda self, x: x
  
      def __call__(self, value):
          filename = value.name
          filename_split = filename.split('.')
          extension = filename_split[-1]
          
          # Decided to require file extensions.
          if len(filename_split) < 2:
              raise ValidationError(
                  "Your file lacks an extension such as .jpg or .png. "
                  "Please re-name it on your computer and re-upload it.",
                  code='no_extension'
              )
  
          # Restrict allowable extensions.
          if extension.lower() not in ALLOWABLE_THUMBNAIL_EXTENSIONS:
              # Format for your viewing pleasure.
              allowable_str = ' '.join(ALLOWABLE_THUMBNAIL_EXTENSIONS)
              raise ValidationError(
                  "Your file is not one of the allowable types: %s" % allowable_str,
                  code='extension_not_allowed'
              )
new_contents: from django.conf import settings
  from django.core.validators import ValidationError
  
  # A list of allowable thumbnail file extensions.
  ALLOWABLE_THUMBNAIL_EXTENSIONS = getattr(
      settings, 'ALLOWABLE_THUMBNAIL_EXTENSIONS', ['png', 'jpg', 'jpeg', 'gif'])
  
  class ImageUploadExtensionValidator(object):
      """
      Perform some basic image uploading extension validation.
      """
      compare = lambda self, a, b: a is not b
      clean   = lambda self, x: x
  
  
      def deconstruct(self):
          path = "athumb.validators.ImageUploadExtensionValidator"
          args = []
          kwargs = {}
          return (path, args, kwargs)
  
  
      def __call__(self, value):
          filename = value.name
          filename_split = filename.split('.')
          extension = filename_split[-1]
          
          # Decided to require file extensions.
          if len(filename_split) < 2:
              raise ValidationError(
                  "Your file lacks an extension such as .jpg or .png. "
                  "Please re-name it on your computer and re-upload it.",
                  code='no_extension'
              )
  
          # Restrict allowable extensions.
          if extension.lower() not in ALLOWABLE_THUMBNAIL_EXTENSIONS:
              # Format for your viewing pleasure.
              allowable_str = ' '.join(ALLOWABLE_THUMBNAIL_EXTENSIONS)
              raise ValidationError(
                  "Your file is not one of the allowable types: %s" % allowable_str,
                  code='extension_not_allowed'
              )
subject: Make ImageUploadExtensionValidator work with django 1.7 migrations