def execute(self):
stack = self._stack<EOL>callbacks = self._callbacks<EOL>self._stack = []<EOL>self._callbacks = []<EOL>deferred = []<EOL>build = self._nested_future<EOL>pipe = self._pipeline(self.connection_name)<EOL>for item, args, kwargs, ref in stack:<EOL><INDENT>f = getattr(pipe, item)<EOL>deferred.append(build(f(*args, **kwargs), ref))<EOL><DEDENT>inject_callbacks = getattr(self.parent, '<STR_LIT>')<EOL>inject_callbacks(deferred + callbacks)<EOL>
execute the commands inside the nested pipeline.
This causes all queued up commands to be passed upstream to the
parent, including callbacks.
The state of this pipeline object gets cleaned up.
:return: