title: Django import error when trying to migrate models from app to app
body: <p>I am having strange problem with import </p>
  
  <p>I have created new app and trying to move some modules there since some of my apps became really big.</p>
  
  <p>I created new app product added it to my settings file and wrote in product/model.py </p>
  
  <pre><code>from django.db import models
  from author.decorators import with_author
  from item.models import ItemGroup
  from item.models import Material
  
  # Create your models here.
  @with_author  
  class Product(models.Model):
      code = models.CharField(max_length=30, unique=True)
      name = models.CharField(max_length=30)
      description = models.TextField(null=True, blank=True)
      creation_time = models.DateTimeField(auto_now_add=True, blank=True)
      itemgroup = models.ForeignKey(ItemGroup, on_delete=models.PROTECT)
      material = models.ForeignKey(Material, on_delete=models.PROTECT)
      keywords = models.CharField(max_length=50,null=True, blank=True)
      valid_from = models.DateTimeField(null=True, blank=True)
      valid_to = models.DateTimeField(null=True, blank=True)
      style1 = models.CharField(max_length=30,null=True, blank=True)
      style2 = models.CharField(max_length=30,null=True, blank=True)
      style3 = models.CharField(max_length=30,null=True, blank=True)
      size = models.CharField(max_length=30,null=True, blank=True)
      dimension = models.CharField(max_length=30,null=True, blank=True)
      color = models.CharField(max_length=30,null=True, blank=True)
  
      def __unicode__(self):
          return u'%s %s %s' % ( self.id, self.code, self.name)
  </code></pre>
  
  <p>when I execute</p>
  
  <pre><code>&gt;python manage.py makemigrations item
  
  &gt;python manage.py makemigrations product
  </code></pre>
  
  <p>I am getting an error </p>
  
  <pre><code>Traceback (most recent call last):
    File "manage.py", line 10, in &lt;module&gt;
      execute_from_command_line(sys.argv)
    File "C:\Users\I812624\dev\mrp\lib\site-packages\django\core\management\__ini
  __.py", line 338, in execute_from_command_line
      utility.execute()
    File "C:\Users\I812624\dev\mrp\lib\site-packages\django\core\management\__ini
  __.py", line 312, in execute
      django.setup()
    File "C:\Users\I812624\dev\mrp\lib\site-packages\django\__init__.py", line 18
   in setup
      apps.populate(settings.INSTALLED_APPS)
    File "C:\Users\I812624\dev\mrp\lib\site-packages\django\apps\registry.py", li
  e 108, in populate
      app_config.import_models(all_models)
    File "C:\Users\I812624\dev\mrp\lib\site-packages\django\apps\config.py", line
  198, in import_models
      self.models_module = import_module(models_module_name)
    File "c:\python27\Lib\importlib\__init__.py", line 37, in import_module
      __import__(name)
    File "C:\Users\I812624\dev\mrp\src\item\models.py", line 13, in &lt;module&gt;
      from product.models import Product
    File "C:\Users\I812624\dev\mrp\src\product\models.py", line 3, in &lt;module&gt;
      from item.models import ItemGroup
  ImportError: cannot import name ItemGroup
  </code></pre>
  
  <p>What could be the problem ?</p>
  
  <p>This is my model of ItemGroup in item </p>
  
  <pre><code>@with_author  
  class ItemGroup(models.Model):
      name = models.CharField(max_length=30)
      description = models.TextField(null=True, blank=True)
      creation_time = models.DateTimeField(auto_now_add=True)
      subcategory = models.ForeignKey(SubCategory, on_delete=models.PROTECT)
      keywords = models.CharField(max_length=50,null=True, blank=True) 
      #hierarchy = TreeForeignKey(Hierarchy,  blank=True, null=True, related_name='cat') 
      def __unicode__(self):
          return u'%s %s' % ( self.id, self.name)
  </code></pre>