diff --git a/README.md b/README.md
index d56e54a..10c63df 100644
--- a/README.md
+++ b/README.md
@@ -1 +1,6 @@
 Repository for CDS-2020 Programming and Promt Engineering II
+
+# Codewars
+* Katas in src/codewars
+|Title|Source|Link|
+|Find the force of gravity between two objects|src/codewars/kata_force_of_gravity.py|https://www.codewars.com/kata/5b609ebc8f47bd595e000627/|
diff --git a/src/codewars/kata_force_of_gravity.py b/src/codewars/kata_force_of_gravity.py
index 3780d5d..0ed4a06 100644
--- a/src/codewars/kata_force_of_gravity.py
+++ b/src/codewars/kata_force_of_gravity.py
@@ -1,5 +1,3 @@
-# https://www.codewars.com/kata/5b609ebc8f47bd595e000627/
-
 units = {
     "kg": 1,
     "g": 1e-3,
diff --git a/src/tutorial/class/class_introduction.py b/src/tutorial/class/class_introduction.py
new file mode 100644
index 0000000..c12f93e
--- /dev/null
+++ b/src/tutorial/class/class_introduction.py
@@ -0,0 +1,10 @@
+class Konto:
+    pass
+
+
+k1 = Konto()
+k2 = Konto()
+
+print(k1)
+print(k2)
+print(k1 is k2)
diff --git a/src/tutorial/class/dataclass_tutorial.py b/src/tutorial/class/dataclass_tutorial.py
new file mode 100644
index 0000000..1a84481
--- /dev/null
+++ b/src/tutorial/class/dataclass_tutorial.py
@@ -0,0 +1,30 @@
+from dataclasses import dataclass
+
+
+@dataclass
+class Student:
+    name: str
+    nr: int
+    sem: int
+
+
+@dataclass
+class Rechteck:
+    breite: float
+    hoehe: float
+
+    def flaeche(self) -> float:
+        return self.breite * self.hoehe
+
+
+# Validierung
+@dataclass
+class Produkt:
+    name: str
+    preis: float
+
+    def __post_init__(self):
+        if not self.name:
+            raise ValueError("...")
+        if self.preis < 0:
+            raise ValueError("...")
diff --git a/src/tutorial/class/hund.py b/src/tutorial/class/hund.py
new file mode 100644
index 0000000..129deb9
--- /dev/null
+++ b/src/tutorial/class/hund.py
@@ -0,0 +1,41 @@
+class Hund:
+    anzahl_hunde = 0
+
+    def __init__(self, name: str, rasse: str, alter: int, gewicht: float):
+        self.name = name
+        self.rasse = rasse
+        self.alter = alter
+        self.gewicht = gewicht
+        Hund.anzahl_hunde += 1
+
+    def __repr__(self):
+        return f"Hund(name={self.name!r}, rasse={self.rasse}, alter={self.alter}, gewicht={self.gewicht}"
+
+    def __str__(self):
+        return f"{self.name} ist ein {self.alter}-jähriger {self.rasse}"
+
+    def bellen(self, n=1) -> int:
+        print(n * "Woof! ")
+
+    def geburtstag(self):
+        self.alter += 1
+        print(
+            f"Alles Gute zum Geburtstag, {self.name}! Du bist jetzt {self.alter} Jahre alt."
+        )
+
+    def ist_welpe(self):
+        if self.alter < 2:
+            print(f"{self.name} ist ein {self.alter}-jähriger Welpe")
+        else:
+            print(f"{self.name} ist ein {self.alter}-jähriger erwachsener Hund")
+
+
+hund1 = Hund(name="Bello", rasse="Pudel", alter=99, gewicht=357)
+hund2 = Hund(name="Dewy", rasse="Labrador", alter=-6, gewicht=1)
+
+print(repr(hund1))
+print(hund2)
+hund2.bellen(3)
+hund1.geburtstag()
+hund2.ist_welpe()
+hund1.ist_welpe()
diff --git a/src/tutorial/class/konto.py b/src/tutorial/class/konto.py
new file mode 100644
index 0000000..8b4927e
--- /dev/null
+++ b/src/tutorial/class/konto.py
@@ -0,0 +1,22 @@
+class Konto:
+    def __init__(self, inhaber, saldo):
+        if not inhaber:
+            raise ValueError("Inhaber darf nicht leer sein")
+        if saldo < 0:
+            raise ValueError("Saldo darf nicht negativ sein")
+        self.inhaber = inhaber
+        self.saldo = saldo
+
+    def einzahlen(self, betrag):
+        self.saldo += betrag
+
+    def abheben(self, betrag):
+        self.saldo -= betrag
+
+
+k = Konto("Alice", 100)
+print(k.saldo)
+k.einzahlen(25)
+print(k.saldo)
+k.abheben(45)
+print(k.saldo)
diff --git a/src/tutorial/class/repr_tutorial.py b/src/tutorial/class/repr_tutorial.py
new file mode 100644
index 0000000..baf16d0
--- /dev/null
+++ b/src/tutorial/class/repr_tutorial.py
@@ -0,0 +1,11 @@
+class Konto:
+    def __init__(self, inhaber, saldo):
+        self.inhaber = inhaber
+        self.saldo = saldo
+
+    def __repr__(self):
+        return f"Konto(inhaber = {self.inhaber!r}, saldo = {self.saldo!r})"
+
+
+k = Konto(" Alice ", 100.0)
+print(k)  # Konto ( inhaber = Alice , saldo =100.0)
diff --git a/src/tutorial/class/str_tutorial.py b/src/tutorial/class/str_tutorial.py
new file mode 100644
index 0000000..db26169
--- /dev/null
+++ b/src/tutorial/class/str_tutorial.py
@@ -0,0 +1,16 @@
+class Konto:
+    def __init__(self, inhaber, saldo):
+        self.inhaber = inhaber
+        self.saldo = saldo
+
+    def __repr__(self):
+        return f"Konto(inhaber = {self.inhaber!r}, saldo = {self.saldo!r})"
+
+    def __str__(self):
+        return f"Konto von {self.inhaber}: CHF {self.saldo:.2f}"
+
+
+k = Konto("Alice", 100.0)
+print(str(k))  # __str__
+print(repr(k))  # __repr__
+print(k)  # bevorzugt __str__ , sonst __repr__