'Returns the resources that would be changed in an update.
Based on the provided template and parameters.
Requires RPC version 1.15 or above.
:param ctxt: RPC context.
:param stack_identity: Name of the stack you wish to update.
:param template: New template for the stack.
:param params: Stack Input Params/Environment
:param files: files referenced from the environment.
:param args: Request parameters/args passed from API
:param environment_files: optional ordered list of environment file
names included in the files dict
:type  environment_files: list or None'

def preview_update_stack(self, ctxt, stack_identity, template, params, files, args, environment_files=None):

    return self.call(ctxt, self.make_msg('preview_update_stack', stack_identity=stack_identity, template=template, params=params, files=files, environment_files=environment_files, args=args), version='1.23')
