diff --git a/39_dataclasses/code.py b/39_dataclasses/code.py
deleted file mode 100644
index 08be01a..0000000
--- a/39_dataclasses/code.py
+++ /dev/null
@@ -1,37 +0,0 @@
-from typing import List
-
-
-class Student:
-    def __init__(self, name: str, grades: List[int] = None):
-        self.name = name
-        self.grades = grades or []
-
-    def take_exam(self, result):
-        self.grades.append(result)
-
-
-bob = Student("Bob")
-bob.take_exam(90)
-print(bob)
-
-# -- as dataclass --
-
-from dataclasses import dataclass, field
-
-
-@dataclass
-class Student:
-    name: str
-    grades: List[int] = field(
-        default_factory=list
-    )  # if we want to run a function, use default_factory and it will run the function to generate the default
-
-    def take_exam(self, result):
-        self.grades.append(result)
-
-
-bob = Student("Bob")
-
-bob.take_exam(90)
-print(bob.grades)
-print(bob)
diff --git a/40_mutability/code.py b/39_mutability/code.py
similarity index 100%
rename from 40_mutability/code.py
rename to 39_mutability/code.py
diff --git a/41_mutable_default_parameters/code.py b/40_mutable_default_parameters/code.py
similarity index 100%
rename from 41_mutable_default_parameters/code.py
rename to 40_mutable_default_parameters/code.py