Feature/dakonr dx sync to (#188)

* return diff to improve dx

* added tests for sync_to and sync_from methods

* run black on init

* moved pylint: disable=too-many-arguments comment

Author: dakonr

diffsync/__init__.py

@@ -526,14 +526,14 @@ def load_from_dict(self, data: Dict):
     # Synchronization between DiffSync instances
     # ------------------------------------------------------------------------------
 
-    def sync_from(
+    def sync_from(  # pylint: disable=too-many-arguments
         self,
         source: "DiffSync",
         diff_class: Type[Diff] = Diff,
         flags: DiffSyncFlags = DiffSyncFlags.NONE,
         callback: Optional[Callable[[Text, int, int], None]] = None,
         diff: Optional[Diff] = None,
-    ):  # pylint: disable=too-many-arguments:
+    ) -> Diff:
         """Synchronize data from the given source DiffSync object into the current DiffSync object.
 
         Args:
@@ -543,6 +543,10 @@ def sync_from(
             callback (function): Function with parameters (stage, current, total), to be called at intervals as the
                 calculation of the diff and subsequent sync proceed.
             diff (Diff): An existing diff to be used rather than generating a completely new diff.
+        Returns:
+            Diff: Diff between origin object and source
+        Raises:
+            DiffClassMismatch: The provided diff's class does not match the diff_class
         """
         if diff_class and diff:
             if not isinstance(diff, diff_class):
@@ -558,14 +562,16 @@ def sync_from(
         if result:
             self.sync_complete(source, diff, flags, syncer.base_logger)
 
-    def sync_to(
+        return diff
+
+    def sync_to(  # pylint: disable=too-many-arguments
         self,
         target: "DiffSync",
         diff_class: Type[Diff] = Diff,
         flags: DiffSyncFlags = DiffSyncFlags.NONE,
         callback: Optional[Callable[[Text, int, int], None]] = None,
         diff: Optional[Diff] = None,
-    ):  # pylint: disable=too-many-arguments
+    ) -> Diff:
         """Synchronize data from the current DiffSync object into the given target DiffSync object.
 
         Args:
@@ -575,8 +581,12 @@ def sync_to(
             callback (function): Function with parameters (stage, current, total), to be called at intervals as the
                 calculation of the diff and subsequent sync proceed.
             diff (Diff): An existing diff that will be used when determining what needs to be synced.
+        Returns:
+            Diff: Diff between origin object and target
+        Raises:
+            DiffClassMismatch: The provided diff's class does not match the diff_class
         """
-        target.sync_from(self, diff_class=diff_class, flags=flags, callback=callback, diff=diff)
+        return target.sync_from(self, diff_class=diff_class, flags=flags, callback=callback, diff=diff)
 
     def sync_complete(
         self,

tests/unit/test_diffsync.py

@@ -42,7 +42,9 @@ def test_diffsync_diff_self_with_no_data_has_no_diffs(generic_diffsync):
 def test_diffsync_sync_self_with_no_data_is_noop(generic_diffsync):
     generic_diffsync.sync_complete = mock.Mock()
     generic_diffsync.sync_from(generic_diffsync)
-    generic_diffsync.sync_to(generic_diffsync)
+    diff = generic_diffsync.sync_to(generic_diffsync)
+    # Check if the returning Diff object has diffs
+    assert not diff.has_diffs()
     # sync_complete() should only be called if something actually changed
     assert not generic_diffsync.sync_complete.called
 
@@ -588,12 +590,13 @@ def test_diffsync_sync_to_w_diff(backend_a, backend_b):
     backend_a.diff_from = mock.Mock()
     backend_a.diff_to = mock.Mock()
     # Perform full sync
-    backend_b.sync_to(backend_a, diff=diff)
+    result_diff = backend_b.sync_to(backend_a, diff=diff)
     # Assert none of the diff methods have been called
     assert not backend_b.diff_from.called
     assert not backend_b.diff_to.called
     assert not backend_a.diff_from.called
     assert not backend_a.diff_to.called
+    assert result_diff.has_diffs()
 
 
 def test_diffsync_sync_from_w_diff(backend_a, backend_b):