Add helper function for django-guardian.

polymorphic/contrib/guardian.py

@@ -0,0 +1,35 @@
+from django.contrib.contenttypes.models import ContentType
+
+
+def get_polymorphic_base_content_type(obj):
+    """
+    Helper function to return the base polymorphic content type id. This should used with django-guardian and the
+    GUARDIAN_GET_CONTENT_TYPE option.
+
+    See the django-guardian documentation for more information:
+
+    https://django-guardian.readthedocs.io/en/latest/configuration.html#guardian-get-content-type
+    """
+    if hasattr(obj, 'polymorphic_model_marker'):
+        try:
+            superclasses = list(obj.__class__.mro())
+        except TypeError:
+            # obj is an object so mro() need to be called with the obj.
+            superclasses = list(obj.__class__.mro(obj))
+
+        polymorphic_superclasses = list()
+        for sclass in superclasses:
+            if hasattr(sclass, 'polymorphic_model_marker'):
+                polymorphic_superclasses.append(sclass)
+
+        # PolymorphicMPTT adds an additional class between polymorphic and base class.
+        if hasattr(obj, 'can_have_children'):
+            root_polymorphic_class = polymorphic_superclasses[-3]
+        else:
+            root_polymorphic_class = polymorphic_superclasses[-2]
+        ctype = ContentType.objects.get_for_model(root_polymorphic_class)
+
+    else:
+        ctype = ContentType.objects.get_for_model(obj)
+
+    return ctype