Add utility for stripping DiffEntry class from diff objects, left wit…

…h only pure python dict objects without attribute access, and test conversion to/from json with this.

nbdime/diff_format.py

@@ -224,6 +224,16 @@ def source_as_string(source):
     return source
 
 
+def to_clean_dicts(di):
+    "Recursively convert dict-like objects to straight python dicts."
+    if isinstance(di, dict):
+        return {k: to_clean_dicts(v) for k, v in di.items()}
+    elif isinstance(di, list):
+        return [to_clean_dicts(v) for v in di]
+    else:
+        return di
+
+
 def to_json_patch(d, path=""):
     """Convert nbdime diff object into the RFC6902 JSON Patch format.
 

nbdime/tests/test_diff_json_conversion.py

@@ -0,0 +1,19 @@
+
+import json
+from nbdime import diff
+from nbdime.diff_format import to_clean_dicts
+
+def test_diff_to_json():
+    a = { "foo": [1,2,3], "bar": {"ting": 7, "tang": 123 } }
+    b = { "foo": [1,3,4], "bar": {"tang": 126, "hello": "world" } }
+    d1 = diff(a, b)
+
+    d2 = to_clean_dicts(d1)
+    assert len(d2) == len(d1)
+    assert all(len(e2) == len(e1) for e1, e2 in zip(d1, d2))
+
+    j = json.dumps(d1)
+    d3 = json.loads(j)
+    assert len(d3) == len(d1)
+    assert all(len(e3) == len(e1) for e1, e3 in zip(d1, d3))
+    assert d2 == d3