Change str function to use json string dump.

data/category.py

@@ -1,6 +1,7 @@
 """File for Category class."""
 
 from typing import Optional
+import json
 
 from data.score import Score, ScoreTime  # pylint: disable=import-error
 
@@ -21,14 +22,7 @@ class Category:
 
     def __str__(self) -> str:
         """Creates a string from the class."""
-        ret_str = f"{self.name}\n"
-        ret_str += f"ascending: {self.ascending}\n"
-        ret_str += f"time_record: {self.time_record}"
-
-        for score in self.scores:
-            ret_str += f"{score}\n"
-
-        return ret_str
+        return json.dumps(self.to_dict(), indent=4)
 
     @property
     def ascending(self) -> bool:
@@ -87,6 +81,7 @@ class Category:
         data = {}
         data["ascending"] = self.ascending
         data["time_record"] = self.time_record
+        data["scores"] = {}
         for score in self.scores:
             data["scores"][score.user] = score.score