# file: runme.py # This file illustrates the cross language polymorphism using directors. import example # CEO class, which overrides Employee::getPosition(). class CEO(example.Manager): def __init__(self, name): example.Manager.__init__(self, name) def getPosition(self): return "CEO" # Create an instance of our employee extension class, CEO. The calls to # getName() and getPosition() are standard, the call to getTitle() uses # the director wrappers to call CEO.getPosition. e = CEO("Alice") e = CEO("Alice") print e.getName(), "is a", e.getPosition() print "Just call her \"%s\"" % e.getTitle() print "----------------------" # Create a new EmployeeList instance. This class does not have a C++ # director wrapper, but can be used freely with other classes that do. list = example.EmployeeList() # EmployeeList owns its items, so we must surrender ownership of objects # we add. This involves first calling the __disown__ method to tell the # C++ director to start reference counting. We reassign the resulting # weakref.proxy to e so that no hard references remain. This can also be # done when the object is constructed, as in: e = # CEO("Alice").__disown__() e = e.__disown__() list.addEmployee(e) print "----------------------" # Now we access the first four items in list (three are C++ objects that # EmployeeList's constructor adds, the last is our CEO). The virtual # methods of all these instances are treated the same. For items 0, 1, and # 2, both all methods resolve in C++. For item 3, our CEO, getTitle calls # getPosition which resolves in Python. The call to getPosition is # slightly different, however, from the e.getPosition() call above, since # now the object reference has been "laundered" by passing through # EmployeeList as an Employee*. Previously, Python resolved the call # immediately in CEO, but now Python thinks the object is an instance of # class Employee (actually EmployeePtr). So the call passes through the # Employee proxy class and on to the C wrappers and C++ director, # eventually ending up back at the CEO implementation of getPosition(). # The call to getTitle() for item 3 runs the C++ Employee::getTitle() # method, which in turn calls getPosition(). This virtual method call # passes down through the C++ director class to the Python implementation # in CEO. All this routing takes place transparently. print "(position, title) for items 0-3:" print " %s, \"%s\"" % (list.get_item(0).getPosition(), list.get_item(0).getTitle()) print " %s, \"%s\"" % (list.get_item(1).getPosition(), list.get_item(1).getTitle()) print " %s, \"%s\"" % (list.get_item(2).getPosition(), list.get_item(2).getTitle()) print " %s, \"%s\"" % (list.get_item(3).getPosition(), list.get_item(3).getTitle()) print "----------------------" # Time to delete the EmployeeList, which will delete all the Employee* # items it contains. The last item is our CEO, which gets destroyed as its # reference count goes to zero. The Python destructor runs, and is still # able to call self.getName() since the underlying C++ object still # exists. After this destructor runs the remaining C++ destructors run as # usual to destroy the object. del list print "----------------------" # All done. print "python exit"