Add str function.

data/score.py

@@ -13,6 +13,9 @@ class Score:
         self._user: str = user
         self._score: int = score
 
+    def __str__(self) -> str:
+        return f"{self.user}: {self.get_str()}"
+
     @property
     def user(self) -> str:
         """Getter for user."""