prefix underscore choice name only if it is dunder, otherwise underscores like sunder are allowed

graphene_django/converter.py

@@ -28,10 +28,18 @@ from .utils import import_single_dispatch
 singledispatch = import_single_dispatch()
 
 
+def _is_dunder(name):
+    """Returns True if a __dunder__ name, False otherwise."""
+    return (len(name) > 4 and
+            name[:2] == name[-2:] == '__' and
+            name[2:3] != '_' and
+            name[-3:-2] != '_')
+
+
 def convert_choice_name(name):
     name = force_text(name).encode('utf8').decode('ascii', 'ignore')
     name = to_const(name)
-    if name.startswith('_'):
+    if _is_dunder(name):
         name = "A%s" % name
     try:
         assert_valid_name(name)

graphene_django/tests/test_converter.py

@@ -199,7 +199,7 @@ def test_field_with_choices_collision():
 def test_field_with_choices_underscore():
     field = models.CharField(
         choices=(
-            ("__amount__", "Amount"),
+            ("_amount__", "Amount"),
             ("__percentage__", "Percentage"),
         ),
     )
@@ -212,8 +212,8 @@ def test_field_with_choices_underscore():
 
     graphene_type = convert_django_field_with_choices(field)
     assert len(graphene_type._meta.enum.__members__) == 2
-    assert graphene_type._meta.enum.__members__["A__AMOUNT__"].value == "__amount__"
+    assert graphene_type._meta.enum.__members__["_AMOUNT__"].value == "_amount__"
-    assert graphene_type._meta.enum.__members__["A__AMOUNT__"].description == "Amount"
+    assert graphene_type._meta.enum.__members__["_AMOUNT__"].description == "Amount"
     assert graphene_type._meta.enum.__members__["A__PERCENTAGE__"].value == "__percentage__"
     assert graphene_type._meta.enum.__members__["A__PERCENTAGE__"].description == "Percentage"
 

graphene_django/tests/test_types.py

@@ -174,7 +174,7 @@ type Reporter {
 enum ReporterAChoice {
   A_1
   A_2
-  A_3
+  _3
 }
 
 enum ReporterReporterType {