TR updates, first round

Author: lpozo

inherit-python-string/lower_string.py

@@ -8,6 +8,7 @@ def __init__(self, string):
 #         instance = super().__new__(cls, string.lower())
 #         return instance
 
+
 # from collections import UserString
 
 

inherit-python-string/mutable_string.py

@@ -3,10 +3,14 @@
 
 class MutableString(UserString):
     def __setitem__(self, index, value):
-        self.data = self.data.replace(self.data[index], value)
+        data_as_list = list(self.data)
+        data_as_list[index] = value
+        self.data = "".join(data_as_list)
 
     def __delitem__(self, index):
-        self.data = self.data[: index - 1] + self.data[index:]
+        data_as_list = list(self.data)
+        del data_as_list[index]
+        self.data = "".join(data_as_list)
 
     def upper(self):
         self.data = self.data.upper()