diff --git a/kyu_4/strings_mix/solution.py b/kyu_4/strings_mix/solution.py
index a73966a0bfa..66b621badd6 100644
--- a/kyu_4/strings_mix/solution.py
+++ b/kyu_4/strings_mix/solution.py
@@ -1,5 +1,6 @@
 """
-Solution for -> Strings Mix
+Solution for -> Strings Mix.
+
 Created by Egor Kostan.
 GitHub: https://github.com/ikostan
 """
@@ -11,6 +12,8 @@
 
 def mix(s1: str, s2: str) -> str:
     """
+    Mix function.
+    
     Given two strings s1 and s2, we want to visualize
     how different the two strings are. We will only
     take into account the lowercase letters (a to z).
@@ -30,28 +33,33 @@ def mix(s1: str, s2: str) -> str:
 
     results: list = []
     for key in keys:
-        if key in s2_results and key in s1_results:
-            if s1_results[key] == s2_results[key]:
-                results.append(f'=:{key * s1_results[key]}')
-            elif s1_results[key] > s2_results[key]:
-                results.append(f'1:{key * s1_results[key]}')
-            else:
-                results.append(f'2:{key * s2_results[key]}')
+        if (
+            key in s2_results
+            and key in s1_results
+            and s1_results[key] == s2_results[key]
+        ):
+            results.append(f'=:{key * s1_results[key]}')
+        elif (
+            key in s2_results
+            and key in s1_results
+            and s1_results[key] > s2_results[key]
+            or (key not in s2_results or key not in s1_results)
+            and key in s1_results
+        ):
+            results.append(f'1:{key * s1_results[key]}')
         else:
-            if key in s1_results:
-                results.append(f'1:{key * s1_results[key]}')
-            else:
-                results.append(f'2:{key * s2_results[key]}')
-
+            results.append(f'2:{key * s2_results[key]}')
     return '/'.join(sort_results(results))
 
 
 def sort_results(results: list) -> list:
     """
+    Sorting results.
+
     The results will be in decreasing order of their length
     and when they have the same length sorted in ascending
     lexicographic order (letters and digits - more precisely
-    sorted by code-point)
+    sorted by code-point).
     :param results:
     :return:
     """
@@ -76,7 +84,8 @@ def sort_results(results: list) -> list:
 
 def get_counters(s: str) -> dict:
     """
-    Get counters
+    Get counters.
+    
     :param s: str
     :return: dict
     """