hash(JsonPatch) raises TypeError when an operation's value is an array or object #217

JsonPatch and PatchOperation define __eq__ and __hash__, but hashing fails for any patch with an array or object value:

>>> import jsonpatch
>>> hash(jsonpatch.JsonPatch([{'op': 'add', 'path': '/a', 'value': []}]))
TypeError: unhashable type: 'list'
>>> hash(jsonpatch.JsonPatch([{'op': 'add', 'path': '/a', 'value': {}}]))
TypeError: unhashable type: 'dict'
>>> hash(jsonpatch.JsonPatch([{'op': 'add', 'path': '/a', 'value': 'x'}]))
1567954150907410962

So such patches can't go into sets or serve as dict keys, while patches with scalar values can.

Cause: PatchOperation.__hash__ returns hash(frozenset(self.operation.items())), which requires every member value to be hashable.

Suggested fix: hash only op, path and from. Operations that compare equal still get equal hashes. Hashing a json.dumps of the whole operation would break that while __eq__ uses Python equality: {'value': 1}, {'value': 1.0} and {'value': True} compare equal but serialize differently (see #216).

Test: JsonPatchProperties.test_equal_patches_have_equal_hashes in property_tests.py is marked @unittest.expectedFailure because of this bug.