Some visitor examples

encapsulated_visitor.py

#!/usr/bin/env python3

# An example visitor where the visitor doesn't know the internal
# structure of the object heirarchy.

class Department:

    def __init__(self, name, employees):
        self._name = name
        self._employees = employees

    def accept(self, visitor):
        visitor.visit_department(self._name)
        for employee in self._employees:
            employee.accept(visitor)


class Employee:

    def __init__(self, name, email):
        self._name = name
        self._email = email

    def accept(self, visitor):
        visitor.visit_employee(self._name, self._email)


class Visitor:

    def visit_department(self, name):
        print('Department: {}'.format(name))

    def visit_employee(self, name, email):
        print('  Employee: {} <{}>'.format(name, email))


if __name__ == '__main__':
    dept = Department('IT', [
        Employee('Adam', '[email protected]'),
        Employee('Bill', '[email protected]'),
        Employee('Cenk', '[email protected]'),
    ])
    dept.accept(Visitor())

type_checking_visitor.py

#!/usr/bin/env python3

# An example visitor using type checking

class Department:

    def __init__(self, name, employees):
        self.name = name
        self.employees = employees

    def accept(self, visitor):
        visitor.visit(self)
        for employee in self.employees:
            employee.accept(visitor)


class Employee:

    def __init__(self, name, email):
        self.name = name
        self.email = email

    def accept(self, visitor):
        visitor.visit(self)


class Visitor:

    def visit(self, thing):
        if isinstance(thing, Department):
            print('Department: {}'.format(thing.name))
        elif isinstance(thing, Employee):
            print('  Employee: {} <{}>'.format(thing.name, thing.email))


if __name__ == '__main__':
    dept = Department('IT', [
        Employee('Adam', '[email protected]'),
        Employee('Bill', '[email protected]'),
        Employee('Cenk', '[email protected]'),
    ])
    dept.accept(Visitor())

visitor.py

#!/usr/bin/env python3

# An example visitor without using type checking

class Department:

    def __init__(self, name, employees):
        self.name = name
        self.employees = employees

    def accept(self, visitor):
        visitor.visit_department(self)
        for employee in self.employees:
            employee.accept(visitor)


class Employee:

    def __init__(self, name, email):
        self.name = name
        self.email = email

    def accept(self, visitor):
        visitor.visit_employee(self)


class Visitor:

    def visit_department(self, dept):
        print('Department: {}'.format(dept.name))

    def visit_employee(self, employee):
        print('  Employee: {} <{}>'.format(employee.name, employee.email))


if __name__ == '__main__':
    dept = Department('IT', [
        Employee('Adam', '[email protected]'),
        Employee('Bill', '[email protected]'),
        Employee('Cenk', '[email protected]'),
    ])
    dept.accept(Visitor())