Mutation of OrderedDict iterator during the loop

.gitignore

@@ -13,3 +13,4 @@ dist/
 build/
 MANIFEST
 .vagrant/
+dj_local_conf.json

.travis.yml

@@ -3,6 +3,7 @@ env:
   - DJ_TEST_HOST="127.0.0.1" DJ_TEST_USER="root" DJ_TEST_PASSWORD="" DJ_HOST="127.0.0.1" DJ_USER="root" DJ_PASSWORD=""
 python:
   - "3.4"
+  - "3.5"
 services: mysql
 install:
   - pip install -r requirements.txt

datajoint/base_relation.py

@@ -357,7 +357,7 @@ def delete(self):
         do_delete = False  # indicate if there is anything to delete
         if config['safemode']:
             print('The contents of the following tables are about to be deleted:')
-        for relation in relations.values():
+        for relation in list(relations.values()):
             count = len(relation)
             if count:
                 do_delete = True

tests/test_cascading_delete.py

@@ -24,6 +24,15 @@ def test_delete_tree():
         A().delete()
         assert_false(A() or B() or B.C() or D() or E() or E.F(), 'incomplete delete')
 
+    @staticmethod
+    def test_stepwise_delete():
+        assert_false(dj.config['safemode'], 'safemode must be off for testing') #TODO: just turn it off instead of warning
+        assert_true(L() and A() and B() and B.C(), 'schema population failed as a precondition to test')
+        B.C().delete()
+        assert_false(B.C(), 'failed to delete child tables')
+        B().delete()
+        assert_false(B(), 'failed to delete the parent table following child table deletion')
+
     @staticmethod
     def test_delete_tree_restricted():
         assert_false(dj.config['safemode'], 'safemode must be off for testing')