title: Cannot import model into my validators.py
body: <p>I am trying to create a custom validation for a model field. My app is named 'Vocabulary' and in there I have a model defined in models.py as below:-</p>
  
  <pre><code>from Vocabulary.validators import word_exists
  
  
  class Vocab(models.Model):
      id  = models.UUIDField(unique=True, primary_key=True)
      word = models.CharField(max_length=33, validators=[word_exists])
      meaning = models.TextField()
  
      def save(self, *args, **kwargs):
          self.id = uuid.uuid4()
          super(Vocab, self).save(*args, **kwargs)
  
      def __str__(self):
          return self.word
  </code></pre>
  
  <p>And inside the validators.py file I have defined custom validator 'word_exists' as follows:-</p>
  
  <pre><code>from Vocabulary.models import Vocab
  from django.core.exceptions import ValidationError
  
  def word_exists(value):
      if Vocab.objects.filter(word=value).exists():
          raise ValidationError("The word already exists!")
  </code></pre>
  
  <p>In this file [validators.py] I keep getting the error that I cannot import the model Vocab. I have done migrations as well but I am not sure what's causing this error. I  am using Django Version 2.0 . Any help is much appreciated.</p>
  
  <p>The App structure is like this:-</p>
  
  <pre><code>Vocabulary[App Name]:-
  -&gt; models.py
  -&gt; validators.py
  </code></pre>