Prevent clearing dict instance when assigning value to itself. fabioc…

…accamo#294

benedict/dicts/base/base_dict.py

@@ -79,6 +79,9 @@ def __setitem__(self, key, value):
             is_dict_item = key in self._dict and isinstance(self._dict[key], dict)
             is_dict_value = isinstance(value, dict)
             if is_dict_item and is_dict_value:
+                if self._dict[key] is value:
+                    # prevent clearing dict instance when assigning value to itself. fix #294
+                    return
                 self._dict[key].clear()
                 self._dict[key].update(value)
                 return

tests/github/test_issue_0294.py

@@ -0,0 +1,20 @@
+import unittest
+
+from benedict import benedict
+
+
+class github_issue_0294_test_case(unittest.TestCase):
+    """
+    This class describes a github issue 0294 test case.
+    https://github.com/fabiocaccamo/python-benedict/issues/294
+
+    To run this specific test:
+    - Run python -m unittest tests.github.test_issue_0294
+    """
+
+    def test_assigning_benedict_element_to_itself_clears_the_element(self):
+        d = benedict({"a": {"b": 1}})
+        d["a"] = d["a"]
+        self.assertEqual(d, {"a": {"b": 1}})
+        d.a = d.a
+        self.assertEqual(d, {"a": {"b": 1}})