'Return dependencies without making any resource plugin calls.
This includes at least all of the dependencies that are explicitly
expressed in the template (via depends_on or an intrinsic function). It
may include implicit dependencies defined by resource plugins, but only
if they have already been calculated.'

def _explicit_dependencies(self):

    if (self._dependencies is None):
        deps = dependencies.Dependencies()
        for res in six.itervalues(self.resources):
            res.add_explicit_dependencies(deps)
        self._dependencies = deps
    return self._dependencies
