Removed usage of a global variable.

tests/forms_tests/models.py

 # -*- coding: utf-8 -*-
 from __future__ import unicode_literals
 
-import os
 import datetime
+import itertools
+import os
 import tempfile
 
 from django.core.files.storage import FileSystemStorage
@@ -10,6 +11,10 @@ from django.db import models
 from django.utils.encoding import python_2_unicode_compatible
 
 
+callable_default_counter = itertools.count()
+callable_default = lambda: next(callable_default_counter)
+
+
 temp_storage_location = tempfile.mkdtemp(dir=os.environ['DJANGO_TEST_TEMP_DIR'])
 temp_storage = FileSystemStorage(location=temp_storage_location)
 
@@ -18,15 +23,6 @@ class BoundaryModel(models.Model):
     positive_integer = models.PositiveIntegerField(null=True, blank=True)
 
 
-callable_default_value = 0
-
-
-def callable_default():
-    global callable_default_value
-    callable_default_value = callable_default_value + 1
-    return callable_default_value
-
-
 class Defaults(models.Model):
     name = models.CharField(max_length=255, default='class default value')
     def_date = models.DateField(default=datetime.date(1980, 1, 1))