Merge pull request #485 from realpython/update_inheritance_composition

Add materials for inheritance-and-composition update

inheritance-and-composition/README.md

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+# Inheritance and Composition
+
+This folder provides the code examples for the Real Python tutorial [Inheritance and Composition: A Python OOP Guide](https://realpython.com/inheritance-composition-python/).
+
+Each of the folders contains the state of the code at the end of the three respective sections:
+
+- **`inheritance/`**: [An Overview of Inheritance in Python](https://realpython.com/inheritance-composition-python/#an-overview-of-inheritance-in-python)
+- **`composition/`**: [Composition in Python](https://realpython.com/inheritance-composition-python/#composition-in-python)
+- **`choosing/`**: [Choosing Between Inheritance and Composition in Python](https://realpython.com/inheritance-composition-python/#choosing-between-inheritance-and-composition-in-python)

inheritance-and-composition/choosing/contacts.py

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+from representations import AsDictionaryMixin
+
+
+class Address(AsDictionaryMixin):
+    def __init__(self, street, city, state, zipcode, street2=""):
+        self.street = street
+        self.street2 = street2
+        self.city = city
+        self.state = state
+        self.zipcode = zipcode
+
+    def __str__(self):
+        lines = [self.street]
+        if self.street2:
+            lines.append(self.street2)
+        lines.append(f"{self.city}, {self.state} {self.zipcode}")
+        return "\n".join(lines)
+
+
+class _AddressBook:
+    def __init__(self):
+        self._employee_addresses = {
+            1: Address("121 Admin Rd.", "Concord", "NH", "03301"),
+            2: Address("67 Paperwork Ave", "Manchester", "NH", "03101"),
+            3: Address("15 Rose St", "Concord", "NH", "03301", "Apt. B-1"),
+            4: Address("39 Sole St.", "Concord", "NH", "03301"),
+            5: Address("99 Mountain Rd.", "Concord", "NH", "03301"),
+        }
+
+    def get_employee_address(self, employee_id):
+        address = self._employee_addresses.get(employee_id)
+        if not address:
+            raise ValueError(employee_id)
+        return address
+
+
+_address_book = _AddressBook()
+
+
+def get_employee_address(employee_id):
+    return _address_book.get_employee_address(employee_id)

inheritance-and-composition/choosing/employees.py

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+from productivity import get_role
+from hr import get_policy
+from contacts import get_employee_address
+from representations import AsDictionaryMixin
+
+
+class _EmployeeDatabase:
+    def __init__(self):
+        self._employees = {
+            1: {"name": "Mary Poppins", "role": "manager"},
+            2: {"name": "John Smith", "role": "secretary"},
+            3: {"name": "Kevin Bacon", "role": "sales"},
+            4: {"name": "Jane Doe", "role": "factory"},
+            5: {"name": "Robin Williams", "role": "secretary"},
+        }
+
+    @property
+    def employees(self):
+        return [Employee(id_) for id_ in sorted(self._employees)]
+
+    def get_employee_info(self, employee_id):
+        info = self._employees.get(employee_id)
+        if not info:
+            raise ValueError(employee_id)
+        return info
+
+
+class Employee(AsDictionaryMixin):
+    def __init__(self, id):
+        self.id = id
+        info = employee_database.get_employee_info(self.id)
+        self.name = info.get("name")
+        self.address = get_employee_address(self.id)
+        self._role = get_role(info.get("role"))
+        self._payroll = get_policy(self.id)
+
+    def work(self, hours):
+        duties = self._role.perform_duties(hours)
+        print(f"Employee {self.id} - {self.name}:")
+        print(f"- {duties}")
+        print("")
+        self._payroll.track_work(hours)
+
+    def calculate_payroll(self):
+        return self._payroll.calculate_payroll()
+
+    def apply_payroll_policy(self, new_policy):
+        new_policy.apply_to_policy(self._payroll)
+        self._payroll = new_policy
+
+
+employee_database = _EmployeeDatabase()

inheritance-and-composition/choosing/hr.py

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+class _PayrollSystem:
+    def __init__(self):
+        self._employee_policies = {
+            1: SalaryPolicy(3000),
+            2: SalaryPolicy(1500),
+            3: CommissionPolicy(1000, 100),
+            4: HourlyPolicy(15),
+            5: HourlyPolicy(9),
+        }
+
+    def get_policy(self, employee_id):
+        policy = self._employee_policies.get(employee_id)
+        if not policy:
+            return ValueError(employee_id)
+        return policy
+
+    def calculate_payroll(self, employees):
+        print("Calculating Payroll")
+        print("===================")
+        for employee in employees:
+            print(f"Payroll for: {employee.id} - {employee.name}")
+            print(f"- Check amount: {employee.calculate_payroll()}")
+            if employee.address:
+                print("- Sent to:")
+                print(employee.address)
+            print("")
+
+
+class PayrollPolicy:
+    def __init__(self):
+        self.hours_worked = 0
+
+    def track_work(self, hours):
+        self.hours_worked += hours
+
+
+class SalaryPolicy(PayrollPolicy):
+    def __init__(self, weekly_salary):
+        super().__init__()
+        self.weekly_salary = weekly_salary
+
+    def calculate_payroll(self):
+        return self.weekly_salary
+
+
+class HourlyPolicy(PayrollPolicy):
+    def __init__(self, hour_rate):
+        super().__init__()
+        self.hour_rate = hour_rate
+
+    def calculate_payroll(self):
+        return self.hours_worked * self.hour_rate
+
+
+class CommissionPolicy(SalaryPolicy):
+    def __init__(self, weekly_salary, commission_per_sale):
+        super().__init__(weekly_salary)
+        self.commission_per_sale = commission_per_sale
+
+    @property
+    def commission(self):
+        sales = self.hours_worked / 5
+        return sales * self.commission_per_sale
+
+    def calculate_payroll(self):
+        fixed = super().calculate_payroll()
+        return fixed + self.commission
+
+
+class LTDPolicy:
+    def __init__(self):
+        self._base_policy = None
+
+    def track_work(self, hours):
+        self._check_base_policy()
+        return self._base_policy.track_work(hours)
+
+    def calculate_payroll(self):
+        self._check_base_policy()
+        base_salary = self._base_policy.calculate_payroll()
+        return base_salary * 0.6
+
+    def apply_to_policy(self, base_policy):
+        self._base_policy = base_policy
+
+    def _check_base_policy(self):
+        if not self._base_policy:
+            raise RuntimeError("Base policy missing")
+
+
+_payroll_system = _PayrollSystem()
+
+
+def get_policy(employee_id):
+    return _payroll_system.get_policy(employee_id)
+
+
+def calculate_payroll(employees):
+    _payroll_system.calculate_payroll(employees)

inheritance-and-composition/choosing/productivity.py

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+class _ProductivitySystem:
+    def __init__(self):
+        self._roles = {
+            "manager": ManagerRole,
+            "secretary": SecretaryRole,
+            "sales": SalesRole,
+            "factory": FactoryRole,
+        }
+
+    def get_role(self, role_id):
+        role_type = self._roles.get(role_id)
+        if not role_type:
+            raise ValueError("role_id")
+        return role_type()
+
+    def track(self, employees, hours):
+        print("Tracking Employee Productivity")
+        print("==============================")
+        for employee in employees:
+            employee.work(hours)
+        print("")
+
+
+class ManagerRole:
+    def perform_duties(self, hours):
+        return f"screams and yells for {hours} hours."
+
+
+class SecretaryRole:
+    def perform_duties(self, hours):
+        return f"does paperwork for {hours} hours."
+
+
+class SalesRole:
+    def perform_duties(self, hours):
+        return f"expends {hours} hours on the phone."
+
+
+class FactoryRole:
+    def perform_duties(self, hours):
+        return f"manufactures gadgets for {hours} hours."
+
+
+_productivity_system = _ProductivitySystem()
+
+
+def get_role(role_id):
+    return _productivity_system.get_role(role_id)
+
+
+def track(employees, hours):
+    _productivity_system.track(employees, hours)

inheritance-and-composition/choosing/program.py

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+from hr import calculate_payroll, LTDPolicy
+from productivity import track
+from employees import employee_database
+
+employees = employee_database.employees
+
+sales_employee = employees[2]
+ltd_policy = LTDPolicy()
+sales_employee.apply_payroll_policy(ltd_policy)
+
+track(employees, 40)
+calculate_payroll(employees)

inheritance-and-composition/choosing/rectangle_square_demo.py

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+class Rectangle:
+    def __init__(self, length, height):
+        self._length = length
+        self._height = height
+
+    @property
+    def area(self):
+        return self._length * self._height
+
+    def resize(self, new_length, new_height):
+        self._length = new_length
+        self._height = new_height
+
+
+class Square(Rectangle):
+    def __init__(self, side_size):
+        super().__init__(side_size, side_size)
+
+
+rectangle = Rectangle(2, 4)
+assert rectangle.area == 8
+
+square = Square(2)
+assert square.area == 4
+
+rectangle.resize(3, 5)
+assert rectangle.area == 15
+
+square.resize(3, 5)
+print(f"Square area: {square.area}")
+
+print("OK!")

inheritance-and-composition/choosing/representations.py

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+class AsDictionaryMixin:
+    def to_dict(self):
+        return {
+            prop: self._represent(value)
+            for prop, value in self.__dict__.items()
+            if not self._is_internal(prop)
+        }
+
+    def _represent(self, value):
+        if isinstance(value, object):
+            if hasattr(value, "to_dict"):
+                return value.to_dict()
+            else:
+                return str(value)
+        else:
+            return value
+
+    def _is_internal(self, prop):
+        return prop.startswith("_")

inheritance-and-composition/composition/contacts.py

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+class Address:
+    def __init__(self, street, city, state, zipcode, street2=""):
+        self.street = street
+        self.street2 = street2
+        self.city = city
+        self.state = state
+        self.zipcode = zipcode
+
+    def __str__(self):
+        lines = [self.street]
+        if self.street2:
+            lines.append(self.street2)
+        lines.append(f"{self.city}, {self.state} {self.zipcode}")
+        return "\n".join(lines)
+
+
+class AddressBook:
+    def __init__(self):
+        self._employee_addresses = {
+            1: Address("121 Admin Rd.", "Concord", "NH", "03301"),
+            2: Address("67 Paperwork Ave", "Manchester", "NH", "03101"),
+            3: Address("15 Rose St", "Concord", "NH", "03301", "Apt. B-1"),
+            4: Address("39 Sole St.", "Concord", "NH", "03301"),
+            5: Address("99 Mountain Rd.", "Concord", "NH", "03301"),
+        }
+
+    def get_employee_address(self, employee_id):
+        address = self._employee_addresses.get(employee_id)
+        if not address:
+            raise ValueError(employee_id)
+        return address