Factor out json and buffer list compare.

Compare deterministic json strings instead of rehydrating them into objects.

ipywidgets/widgets/widget.py

@@ -17,7 +17,7 @@
     Undefined)
 from ipython_genutils.py3compat import string_types, PY3
 from IPython.display import display
-from json import loads as jsonloads, dumps as jsondumps
+from json import dumps as jsondumps
 
 from base64 import standard_b64decode, standard_b64encode
 
@@ -127,6 +127,35 @@ def _remove_buffers(state):
     state = _separate_buffers(state, [], buffer_paths, buffers)
     return state, buffer_paths, buffers
 
+def _buffer_list_equal(a, b):
+    """Compare two lists of buffers for equality.
+
+    Used to decide whether two sequences of buffers (memoryviews,
+    bytearrays, or python 3 bytes) differ, such that a sync is needed.
+
+    Returns True if equal, False if unequal
+    """
+    if len(a) != len(b):
+        return False
+    if a == b:
+        return True
+    for ia, ib in zip(a, b):
+        # Check byte equality:
+        # NOTE: Simple ia != ib does not always work as intended, as
+        # e.g. memoryview(np.frombuffer(ia, dtype='float32')) !=
+        # memoryview(np.frombuffer(b)), since the format info differs.
+        # However, since we only transfer bytes, we use `tobytes()`.
+        ia_bytes = ia.tobytes() if isinstance(ia, memoryview) else ia
+        ib_bytes = ib.tobytes() if isinstance(ib, memoryview) else ib
+        if ia_bytes != ib_bytes:
+            return False
+    return True
+
+def _json_equal(a, b):
+    """Compare the JSON strings generated by two objects."""
+    return (jsondumps(a, separators=(',',':'), sort_keys=True, allow_nan=False)
+            == jsondumps(b, separators=(',',':'), sort_keys=True, allow_nan=False))
+
 class LoggingHasTraits(HasTraits):
     """A parent class for HasTraits that log.
     Subclasses have a log trait, and the default behavior
@@ -485,30 +514,6 @@ def _compare(self, a, b):
         else:
             return a == b
 
-    def _buffer_list_equal(self, a, b):
-        """Compare two lists of buffers for equality.
-
-        Used to decide whether two sequences of buffers (memoryviews,
-        bytearrays, or python 3 bytes) differ, such that a sync is needed.
-
-        Returns True if equal, False if unequal
-        """
-        if len(a) != len(b):
-            return False
-        if a == b:
-            return True
-        for ia, ib in zip(a, b):
-            # Check byte equality:
-            # NOTE: Simple ia != ib does not always work as intended, as
-            # e.g. memoryview(np.frombuffer(ia, dtype='float32')) !=
-            # memoryview(np.frombuffer(b)), since the format info differs.
-            # However, since we only transfer bytes, we use `tobytes()`.
-            ia_bytes = ia.tobytes() if isinstance(ia, memoryview) else ia
-            ib_bytes = ib.tobytes() if isinstance(ib, memoryview) else ib
-            if ia_bytes != ib_bytes:
-                return False
-        return True
-
     def set_state(self, sync_data):
         """Called when a state is received from the front-end."""
         # The order of these context managers is important. Properties must
@@ -628,9 +633,9 @@ def _should_send_property(self, key, value):
             split_value = _remove_buffers({ key: to_json(value, self)})
             split_lock = _remove_buffers({ key: self._property_lock[key]})
             # Compare state and buffer_paths
-            if (jsonloads(jsondumps(split_value[0])) == jsonloads(jsondumps(split_lock[0]))
+            if (_json_equal(split_value[0], split_lock[0])
                 and split_value[1] == split_lock[1]
-                and self._buffer_list_equal(split_value[2], split_lock[2])):
+                and _buffer_list_equal(split_value[2], split_lock[2])):
                 return False
         if self._holding_sync:
             self._states_to_send.add(key)