improve types and add clarity around what happens inside presume

xoeye · Sep 29, 2021 · a8ec035 · a8ec035
1 parent 8a440b4
commit a8ec035
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Showing 2 changed files with 7 additions and 10 deletions.
diff --git a/dev-utils/watch_ddb_stream.py b/dev-utils/watch_ddb_stream.py
@@ -14,8 +14,8 @@
 DYNAMODB_STREAMS = make_dynamodb_stream_images_multicast()
 
 
-def make_accept_stream_images(item_slicer: Callable[[ItemImages], str]):
-    def accept_stream_item(images: ItemImages):
+def make_accept_stream_images(item_slicer: Callable[[ItemImages], dict]):
+    def accept_stream_item(images: ItemImages) -> None:
         old, new = images
         if not old:
             print(f"New item: {item_slicer(images)}")  # type: ignore
@@ -34,7 +34,7 @@ def make_key_slicer(table):
     except ValueError:
         range_key = ""
 
-    def extract_primary_key(images: ItemImages):
+    def extract_primary_key(images: ItemImages) -> dict:
         old, new = images
         item = new or old
         assert item is not None
@@ -48,7 +48,7 @@ def extract_primary_key(images: ItemImages):
 
 
 def make_item_slicer(key_slicer, attribute_names):
-    def item_slicer(images: ItemImages):
+    def item_slicer(images: ItemImages) -> dict:
         old, new = images
         if not new:
             new = dict()

diff --git a/xoto3/dynamodb/write_versioned/specify.py b/xoto3/dynamodb/write_versioned/specify.py
@@ -61,16 +61,13 @@ def presume(
         )
     hkey = hashable_key(item_key)
     if hkey not in table_data.items:
+        item_value = dynamodb_prewrite(item_value, prewrite_transform) if item_value else None
+        # this prewrite makes sure the value looks like it could have come out of DynamoDB.
         return VersionedTransaction(
             tables={
                 **transaction.tables,
                 table_name: _TableData(
-                    items={
-                        **table_data.items,
-                        hkey: dynamodb_prewrite(item_value, prewrite_transform)
-                        if item_value
-                        else item_value,
-                    },
+                    items={**table_data.items, hkey: item_value},
                     effects=table_data.effects,
                     key_attributes=table_data.key_attributes,
                 ),