def prepare(self):
        """
        Called just before the task is executed.

        This is mainly intended to give the target Nodes a chance to
        unlink underlying files and make all necessary directories before
        the Action is actually called to build the targets.
        """
        global print_prepare
        T = self.tm.trace
        if T: T.write(self.trace_message(u'Task.prepare()', self.node))

        # Now that it's the appropriate time, give the TaskMaster a
        # chance to raise any exceptions it encountered while preparing
        # this task.
        self.exception_raise()

        if self.tm.message:
            self.display(self.tm.message)
            self.tm.message = None

        # Let the targets take care of any necessary preparations.
        # This includes verifying that all of the necessary sources
        # and dependencies exist, removing the target file(s), etc.
        #
        # As of April 2008, the get_executor().prepare() method makes
        # sure that all of the aggregate sources necessary to build this
        # Task's target(s) exist in one up-front check.  The individual
        # target t.prepare() methods check that each target's explicit
        # or implicit dependencies exists, and also initialize the
        # .sconsign info.
        executor = self.targets[0].get_executor()
        if executor is None:
            return
        executor.prepare()
        for t in executor.get_action_targets():
            if print_prepare:
                print("Preparing target %s..."%t)
                for s in t.side_effects:
                    print("...with side-effect %s..."%s)
            t.prepare()
            for s in t.side_effects:
                if print_prepare:
                    print("...Preparing side-effect %s..."%s)
                s.prepare()
Called just before the task is executed.

        This is mainly intended to give the target Nodes a chance to
        unlink underlying files and make all necessary directories before
        the Action is actually called to build the targets.