title: Django -- can't import my own models
body: <p>I have several Django apps, all within one project directory. Each app has a <code>models.py</code> file with a bunch of models. I have been importing models from one app to the other with no problem, specifically to create a new model with a foreign key field, pointing to the model in the other app. No problem so far. </p>
  
  <p>I decided to create a new model. It has 4 <code>ForeignKey</code> fields, each pointing to a different model in a different app. Straight forward. However, when I try to use <code>south</code> to migrate the schema to the database, it tells me that it can't import my models. Why?!</p>
  
  <p>So, this is my new model:</p>
  
  <pre><code>class Action_Tracker(models.Model):
      dateOfAction = models.DateField(verbose_name = 'Date of Action')
      user = models.CharField(max_length=30, verbose_name = 'Action completed by')
      sys = models.ForeignKey(System, verbose_name='For System')
      wo = models.ForeignKey(Work_Order, verbose_name='Associated WO', blank=True, null=True)
      inv = models.ForeignKey(Invoice, verbose_name = 'Associated Invoice', blank=True, null=True)
      subdT = models.ForeignKey(SUBD_Tracker, verbose_name = 'Associated SUBD Tracker', blank=True, null=True)
      notes = models.TextField(verbose_name='Notes of Action', blank=True, null=True)
  
      def __unicode__(self):
          return u'%s -- %s' % (self.dateOfAction, self.notes)
  
      class Meta:
          orering = ['dateOfAction']
  </code></pre>
  
  <p>At the top of this <code>models.py</code> file I have the following imports:</p>
  
  <pre><code>from django.db import models
  from django.forms import ModelForm, forms
  from staff.models import Employee, Position
  from work_orders.models import Work_Order, SUBD_Tracker
  from invoices.models import Invoice
  </code></pre>
  
  <p>From what I can tell, I <em>am</em> importing these correctly. However, when I try to do a schema migration, I get the following error:</p>
  
  <pre><code>File "/srv/www/cpm/../cpm/systems/models.py", line 4, in &lt;module&gt;
    from work_orders.models import Work_Order, SUBD_Tracker
  File "/srv/www/cpm/work_orders/models.py", line 5, in &lt;module&gt;
    from systems.models import System
  File "/srv/www/cpm/systems/models.py", line 4, in &lt;module&gt;
    from work_orders.models import Work_Order, SUBD_Tracker
  ImportError: cannot import name Work_Order
  </code></pre>
  
  <p>Any idea what is going wrong here??</p>
  
  <p>Thanks</p>
  
  <p><strong>EDIT -- Upon Request</strong> </p>
  
  <p>I'm posting the work_order <code>models.py</code> code as requested (at least, the relevant parts):</p>
  
  <pre><code>from django.db import models
  from django.forms import ModelForm, forms
  from django import forms
  from products.models import Product
  from systems.models import System
  from labour.models import Labour_Costs
  from staff.models import Employee
  from datetime import date
  import datetime
  
  class Work_Order(models.Model):
      IS_COMPLETE_CHOICES = (
          ('Y', 'Yes'),
          ('N', 'No'),
      )
  
      INVOICE_CREATED_CHOICES = (
          ('Y', 'Yes, mark WO complete and generate invoice (if applicable)'),
          ('N', 'No, just save these changes'),
      )
  
      WO_TYPE_CHOICES = (
          ('M', 'Mechanical'),
          ('I', 'Install'),
          ('S', 'Show'),
          ('R', 'Service'),
          ('B', 'Blow down'),
          ('U', 'Start up'),
      )
  
      woID = models.CharField(max_length = 25, primary_key = True, verbose_name = 'Work Order ID')
      woType = models.CharField(max_length = 2, verbose_name = 'WO Type', default='R', choices = WO_TYPE_CHOICES)
      systemID = models.ForeignKey(System, verbose_name = 'System ID')
      notesToCrew = models.TextField(blank = True, null = True, verbose_name = 'Notes to Crew')
      dateWOCreated = models.DateField(blank = True, null = True, default=datetime.date.today(), verbose_name = 'Date Created')
      dateWORequired = models.DateField(blank = True, null = True, verbose_name = 'Date Required')
      dateCompleted = models.DateField(blank = True, null = True, verbose_name = 'Date Completed')
      numDays = models.DecimalField(max_digits = 3, decimal_places = 0, verbose_name = 'Number of Days to Complete', blank = True, null = True)
      numHours = models.DecimalField(max_digits = 3, decimal_places = 2, verbose_name = 'Number of Hours to Complete', blank = True, null = True)
      isComplete = models.CharField (max_length = 3, default = 'N', verbose_name = 'Set WO as Completed?', choices = IS_COMPLETE_CHOICES)
      isScheduled = models.CharField (max_length = 3, default = 'N', verbose_name = 'Is WO scheduled?', choices = IS_COMPLETE_CHOICES)
      isReqSoon = models.BooleanField(default=False, verbose_name='Is WO Required soon') #This flag will be set in a function to indicate that the WO is reqd within the current week/few days, whatever
      problemDescription = models.TextField(verbose_name = 'Problem Description', blank = True, null = True)
      resolution = models.TextField(verbose_name = 'Resolution', blank = True, null = True)
      serviceFromBD = models.TextField(verbose_name = 'Service issues noticed', blank = True, null = True)
      serviceFromBDEstTime = models.DecimalField(max_digits = 3, decimal_places = 2, verbose_name = 'Est. Time to Repair', blank = True, null = True)
      numWorkers = models.DecimalField(max_digits = 3, default=1, decimal_places = 0, verbose_name = 'Number of Workers Required', blank = True, null = True)
      invoiceCreated = models.CharField (max_length = 3, default = 'N', verbose_name = 'Generate Invoice?', choices = INVOICE_CREATED_CHOICES)
  
      def __unicode__(self):
          return u'%s - %s' % (self.woID, self.systemID.systemAddress)
  
      class Meta:
          ordering = ['woID']
  
  
  class SUBD_Tracker(models.Model):
      SUBD_CHOICES = (
          ('U', 'Startup'),
          ('B', 'Blowdown'),
      )
  
      sys = models.ForeignKey(System, verbose_name = 'Related System')
      subd = models.CharField(max_length=1, verbose_name = 'SU or BD', choices = SUBD_CHOICES)
      ssn = models.CharField(max_length=5, verbose_name = 'Season')
      approved = models.BooleanField(verbose_name = 'Approved', default = False)
      declined = models.BooleanField(verbose_name = 'Declined', default = False)
      cancelled = models.BooleanField(verbose_name = 'Cancel', default = False)
      firstNoticeSent = models.BooleanField(verbose_name = 'First Notice Sent?', default = False)
      secondNoticeSent = models.BooleanField(verbose_name = 'Second Notice Sent?', default = False)
      wo = models.ForeignKey(Work_Order, verbose_name = 'Related WO', blank = True, null = True)
  
      def __unicode__(self):
          if self.subd == 'U':
              return u'%s: Startup - %s' % (self.sys, self.ssn)
          else:
              return u'%s: Blowdown - %s' % (self.sys, self.ssn)
  
      class Meta:
          ordering = ['sys']
  </code></pre>