diff --git a/ziffers/common.py b/ziffers/common.py
index e2771a5..d3deead 100644
--- a/ziffers/common.py
+++ b/ziffers/common.py
@@ -1,19 +1,18 @@
-def flatten(arr) -> list:
+def flatten(arr: list) -> list:
     """Flattens array"""
     return (
         flatten(arr[0]) + (flatten(arr[1:]) if len(arr) > 1 else [])
-        if type(arr) is list
-        else [arr]
+        if isinstance(arr, list) else [arr]
     )
 
 
-def sum_dict(arr) -> dict:
-    """Sums array of dicts: [{a:3,b:3},{b:1}] -> {a:3,b:4}"""
+def sum_dict(arr: list[dict]) -> dict:
+    """Sums a list of dicts: [{a:3,b:3},{b:1}] -> {a:3,b:4}"""
     result = arr[0]
-    for hash in arr[1:]:
+    for element in arr[1:]:
         for key in hash.keys():
             if key in result:
-                result[key] = result[key] + hash[key]
+                result[key] = result[key] + element[key]
             else:
-                result[key] = hash[key]
+                result[key] = element[key]
     return result