def paths_on_pythonpath(paths):
        """
        Add the indicated paths to the head of the PYTHONPATH environment
        variable so that subprocesses will also see the packages at
        these paths.

        Do this in a context that restores the value on exit.
        """
        nothing = object()
        orig_pythonpath = os.environ.get('PYTHONPATH', nothing)
        current_pythonpath = os.environ.get('PYTHONPATH', '')
        try:
            prefix = os.pathsep.join(unique_everseen(paths))
            to_join = filter(None, [prefix, current_pythonpath])
            new_path = os.pathsep.join(to_join)
            if new_path:
                os.environ['PYTHONPATH'] = new_path
            yield
        finally:
            if orig_pythonpath is nothing:
                os.environ.pop('PYTHONPATH', None)
            else:
                os.environ['PYTHONPATH'] = orig_pythonpath

        Add the indicated paths to the head of the PYTHONPATH environment
        variable so that subprocesses will also see the packages at
        these paths.

        Do this in a context that restores the value on exit.
        
product/gradle-plugin/src/main/python/setuptools/command/test.py