diff --git a/9 - solid/dependency-inversion-after-comp.py b/9 - solid/dependency-inversion-after-comp.py
new file mode 100644
index 0000000..6c06b63
--- /dev/null
+++ b/9 - solid/dependency-inversion-after-comp.py	
@@ -0,0 +1,101 @@
+#!/usr/bin/env python3
+
+
+class Order:
+
+    def __init__(self):
+        self.items = []
+        self.quantities = []
+        self.prices = []
+        self.status = "open"
+
+    def add_item(self, name, quantity, price):
+        self.items.append(name)
+        self.quantities.append(quantity)
+        self.prices.append(price)
+
+    def total_price(self):
+        total = 0
+        for i in range(len(self.prices)):
+            total += self.quantities[i] * self.prices[i]
+        return total
+
+
+class SMSAuth:
+
+    def __init__(self):
+        self.authorized = False
+
+    def verify_code(self, code):
+        print(f'Verifying SMS code {code!r}')
+        self.authorized = True
+
+
+class GoogleAuth:
+
+    def __init__(self):
+        self.authorized = False
+
+    def verify_code(self, code):
+        print(f'Verifying GoogleAuth code {code!r}')
+        self.authorized = True
+
+
+class NotARobotAuth:
+
+    def __init__(self):
+        self.authorized = False
+
+    def not_a_robot(self):
+        self.authorized = True
+
+
+class DebitPaymentProcessor:
+
+    def __init__(self, security_code, authorizer):
+        self.security_code = security_code
+        self.authorizer = authorizer
+
+    def pay(self, order):
+        if not self.authorizer.authorized:
+            raise Exception("Not authorized")
+        print("Processing debit payment type")
+        print(f"Verifying security code: {self.security_code}")
+        order.status = "paid"
+
+
+class CreditPaymentProcessor:
+
+    def __init__(self, security_code):
+        self.security_code = security_code
+
+    def pay(self, order):
+        print("Processing credit payment type")
+        print(f"Verifying security code: {self.security_code}")
+        order.status = "paid"
+
+
+class PaypalPaymentProcessor:
+
+    def __init__(self, email_address, authorizer):
+        self.email_address = email_address
+        self.authorizer = authorizer
+
+    def pay(self, order):
+        if not self.authorizer.authorized:
+            raise Exception("Not authorized")
+        print("Processing paypal payment type")
+        print(f"Using email address: {self.email_address}")
+        order.status = "paid"
+
+
+order = Order()
+order.add_item("Keyboard", 1, 50)
+order.add_item("SSD", 1, 150)
+order.add_item("USB cable", 2, 5)
+
+print(order.total_price())
+authorizer = GoogleAuth()
+authorizer.verify_code(9445)
+processor = PaypalPaymentProcessor("hi@arjancodes.com", authorizer)
+processor.pay(order)