Update models.py for python3

according to https://docs.djangoproject.com/en/1.11/topics/python3/ I added compatibility for python3

Author: jiargei

eav/models.py

@@ -32,6 +32,7 @@
 Classes
 -------
 '''
+from __future__ import unicode_literals
 from builtins import object
 
 
@@ -44,6 +45,7 @@
 from django.contrib.sites.models import Site
 from django.contrib.sites.managers import CurrentSiteManager
 from django.conf import settings
+from django.utils.encoding import python_2_unicode_compatible
 
 from .validators import *
 from .fields import EavSlugField, EavDatatypeField
@@ -81,9 +83,10 @@ class EnumValue(models.Model):
     value = models.CharField(_(u"value"), db_index=True,
                              unique=True, max_length=50)
 
-    def __unicode__(self):
+    @python_2_unicode_compatible
+    def __str__(self):
         return self.value
-
+       
 
 class EnumGroup(models.Model):
     '''
@@ -98,7 +101,8 @@ class EnumGroup(models.Model):
 
     enums = models.ManyToManyField(EnumValue, verbose_name=_(u"enum group"))
 
-    def __unicode__(self):
+    @python_2_unicode_compatible
+    def __str__(self):
         return self.name
 
 
@@ -318,7 +322,8 @@ def save_value(self, entity, value):
             value_obj.value = value
             value_obj.save()
 
-    def __unicode__(self):
+    @python_2_unicode_compatible
+    def __str__(self):
         return u"%s.%s (%s)" % (self.content_type, self.name, self.get_datatype_display())
 
 
@@ -401,7 +406,8 @@ def _set_value(self, new_value):
 
     value = property(_get_value, _set_value)
 
-    def __unicode__(self):
+    @python_2_unicode_compatible
+    def __str__(self):
         return u"%s - %s: \"%s\"" % (self.entity, self.attribute.name,
                                      self.value)