Django/Python Circular model reference

Question

Ok So I'm TRYING to write nice organized code and actually making seperate django apps instead of lumping everything together into 1. My problem is that I have 3 apps that each reference 1 other model from the next app. So basically I have an endless loop, App A needs to know about B.models.something1 , App B needs to know about C.models.Somthing2, and App C needs to know about A.models.something3 . This of course will not run, for those wondering if this is actually a problem :) .Is there anything resembling a predeclaration of classes so python will know that the classes actually exist?

Thanks.

EDIT: More Code: Unfortunatly the nature and models of my project are confidential so I'll have to change the names to reflect something completely different , but the code will remain the same.

teacher/models.py

 from django.db import models
 from myapp.student.models import *
 from django.contrib.auth.models import User
 class Teacher(models.Model):
     """(description)"""
     user = models.ForeignKey(User)
     name = models.CharField(max_length=100)
     phone = models.CharField(max_length=13)
     phone_ext = models.CharField(blank=True, max_length=5)
     fax = models.CharField(blank=True, max_length=13)
     fax_ext = models.CharField(blank=True, max_length=100)
     url = models.URLField(blank=True, verify_exists=True)
     complaint = models.ManyToManyField(Complaint)
     city = models.CharField(blank=True, max_length=100)
     state = models.CharField(blank=True, max_length=100)
     postal_code = models.CharField(blank=True, max_length=15)
     location = models.ManyToManyField(Location)
     def __unicode__(self):
         return self.name
 class Location(models.Model):
     """(description)"""
     city = models.CharField(blank=True, max_length=100)
     state = models.CharField(blank=True, max_length=100)
     country = models.CharField(blank=False, max_length=100)
     def __unicode__(self):
         return self.city + ", " + self.state +", "+self.country

student/models.py

 from django.db import models
 from django.contrib.auth.models import User
 from myapp.school.models import School

 class Student(models.Model):
     """(Student description)"""
     user = models.ForeignKey(User)
     country = models.CharField(max_length=100)
     state = models.CharField(max_length=100)
     city = models.CharField(max_length=100)
     locale = models.CharField(blank=False, max_length=5)
     learningtype = models.CharField(blank=True, max_length=100)
     sites = models.TextField(blank=True)
     def __unicode__(self):
         return str(self.user)

 class Complaint(models.Model):
     """(Complaint description)"""
     student = models.ForeignKey(Student)
     site = models.ForeignKey(School)
     complaint = models.TextField(blank=False)
     def __unicode__(self):
         return str(self.site)

school/models.py

 from django.db import models
 from myapp.teacher.models import Location
 class School(models.Model):
     """(School description)"""
     name = models.CharField(max_length=100)
     url = models.URLField(verify_exists=True)
     img = models.ImageField(upload_to="casion_img/")
     rating = models.FloatField()
     description = models.CharField(blank=True, max_length=300)
     goodstanding = models.BooleanField(default=True)
     location = models.ForeignKey(Location)
     def __unicode__(self):
         return self.name

So here's what I'm getting:

File "/Users/userzero/django/myapp/school/models.py", line 2, in from teacher.models import Location File "/Users/userzero/django/myapp/teacher/models.py", line 2, in from student.models import Complaint File "/Users/userzero/django/myapp/student/models.py", line 3, in from school.models import School File "/Users/userzero/django/myapp/casino/models.py", line 2, in from teacher.models import Location ImportError: cannot import name Location

Answer 1

From the docs:

To refer to models defined in another application, you can explicitly specify a model with the full application label. For example, if the Manufacturer model above is defined in another application called production, you'd need to use:

class Car(models.Model):
     manufacturer = models.ForeignKey('production.Manufacturer')

This sort of reference can be useful when resolving circular import dependencies between two applications.

So for your apps, try changing e.g.

 location = models.ForeignKey(Location) 

to

 location = models.ForeignKey('Location')

Note that if this model is in a different app then you need to specify that too (thanks @Bran for pointing this out), e.g.

 location = models.ForeignKey('teacher.Location')